He beat that Obamacare deadline. Did you?

New York City resident Nicolas Karlson was happy to be one of at least 2.5 million people who beat a major Obamacare enrollment deadline last week, but he's going to be paying a lot more for health insurance next year because of it.

To cover himself, his wife, Monica, and their three children, 45-year-old Karlson will go from paying $1,805 every three months for their long-standing Aetna plan, to a new one from New York State's Obamacare exchange that will cost them $1,221.60 per month, or more than 100 percent more than his old plan cost.

That steep bump in price is a result of Aetna's reacting to a feature in the Affordable Care Act, a law that Karlson said of with a laugh, "I literally had no idea that it would affect me at all."

That feature, as well as others in the ACA, motivated millions of people since Nov. 15 to sign up for health plans sold on government-run Obamacare marketplaces such as HealthCare.gov. The deadline for choosing plans that take effect Jan. 1 was Dec. 15 for federally run HealthCare.gov, which serves two-thirds of the U.S., but a number of state-run exchanges extended their own deadlines.

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Tuesday is the deadline for Massachusetts, Washington state and Rhode Island. Exchanges in three other states (Vermont, Minnesota and Hawaii) have given residents until Dec. 31 to select plans that take effect the next day.

The deadline for the New York State of Health exchange originally was Dec. 15, but officials extended it until last Saturday because of heavy snowstorms that affected the western part of the state last month.

People speak with an agent from Sunshine Life and Health Advisors, as they discuss plans available from the Affordable Care Act on Dec. 15, 2014, in Miami.
Getty Images
People speak with an agent from Sunshine Life and Health Advisors, as they discuss plans available from the Affordable Care Act on Dec. 15, 2014, in Miami.

Karlson, who runs a commercial production company, was unaware that New York had extended its deadline by five days, so he was scrambling two weeks ago to get new insurance.

For six years or so, Karlson and his wife had an Aetna plan from a former employer of hers. Monica Karlson had kept the coverage via COBRA, which allows individuals to maintain their originally employer-provided coverage by paying for it directly. At some point the plan converted from COBRA, but the costs remained low.

Several months ago, Aetna sent the Karlsons a letter "saying that our current plan is being canceled, and to go to the website and review plans that are available," Nicolas Karlson said.

Despite that, the alternative were not posted for more than a month.

And when Karlson looked at them, he was surprised.

To get comparable coverage, he was looking at plans that cost between around $20,300 and $23,612 annually.

He then called an Aetna rep.

"I said, 'Right now, I'm paying $8,000 per year; what am I missing?' " Karlson recounted. "He said, 'That plan is discontinued.' He also said, 'I don't think that's what you're paying.' "

"He said, '$1,800 per month,' and I said, 'No, $1,800 per quarter.' He said, 'Wow, you're really lucky,' " Karlson said.

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But Karlson's luck had come to an end.

The Affordable Care Act mandated a set of "essential health benefits" that all insurance plans had to cover, which included preventative services, ER visits, pediatric vision and dental care and mental health care. That mandate rendered many plans non-compliant with the law.

Pre-existing plans, or grandfathered plans, were allowed to continue under the ACA, but only if insurers made no significant changes to coverage. And in response to the troubled launch of HealthCare.gov last year, the Obama administration has allowed the option of other non-compliant plans continuing through 2017.

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But not all states or insurers have taken up that option, or maintained it for their customers.

Although Karlson's non-compliant plan was allowed to continue in Obamacare's first year, Aetna pulled the plug for 2015.

"As noted in the letter to our customer, we discontinued this plan, as we have others," said Aetna spokeswoman Susan Millerick. "Our intent is to offer individuals a selection of ACA-compliant plans. We believe the marketplaces now offer a stable experience that offers consumers the opportunity to shop, compare and buy plans and we also have been working with customers to find a new Aetna plan if they choose."

"We began this process in 2013 and have been updating our portfolio over time, so we have not been releasing specific information about the number of plans that have been discontinued, but I can tell you that this is a small subset of our individual customer base, which is a small portion of Aetna's overall membership," Millerick said.

Despite the big increase in price, Karlson was ready to stay with an Aetna plan.

That changed when he called a rep for Aetna "to check on something. That was when the person I spoke to said, 'Oh, just so you know, there's no out-of-network coverage,' " Karlson recalled.

In other words, he'd have to pay out of pocket for any doctors who weren't in Aetna's network of providers.

That was a problem for him because "a good deal of our doctors are out of network" and their services had been covered by the old plan, Karlson said. By this time, it was Dec. 12, three days away from what he believed to be the sign-up deadline.

He reached out to someone he knew who had dealt with insurance before, who referred him to an investment adviser name Brett Sigler, of Client Focused Advisors in New York. Sigler and his colleagues last year got certified as brokers for the New York State of Health.

Sigler told CNBC that while "we saw there was an opportunity where a lot of people were going to need help," other than putting out the word in a networking group he was associated with, he didn't really solicit business actively.

Despite that, Sigler's gotten Obamacare business this year from Karlson and about 100 other people, essentially from word of mouth.

"It's been way more than I anticipated," Sigler said. "I'll get calls from people that I've never met before."

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"I've seen a lot of frustration with just how complicated the whole process is. Their plans were just uprooted, and they get looking into figuring out what they should be doing," Sigler said. "The website can be intimidating for people to figure out."

"My last two weeks have been insane," he said, referring to the number of health insurance sign-ups he has handled. He noted that about 15 people contacted him past the original Dec. 15 New York deadline for coverage as of Jan. 1, with some unaware when the deadline was, extended or otherwise. The final open-enrollment deadline for any 2015 coverage is Feb. 15.

Sigler worked with Karlson and got him a new family plan that costs $1,221.60 per month from Health Republic Insurance, a co-op, or consumer-operated and -oriented insurer that was started to serve the new Obamacare market.

On Monday, after having enrolled in the new coverage, Karlson said he felt somewhat ambivalent about the experience of having had to purchase an Obamacare plan.

"It's like, I'm happy that I have insurance, but I wish I could have the insurance that I want," he said. "I feel I can adapt to whatever I have, and we are, but, I guess it's like I didn't realize I had a good thing."

Karlson said he and his wife were talking about getting appointments for some of their existing doctors before the New Year, in the event they never are able to go to them again with coverage under the new plan. "I'm just kind of annoyed that it's not as simple as it once was," he said.

By CNBC's Dan Mangan.