Socked with more than a quarter-million dollars in medical bills despite having full health coverage, a city lawyer decided to take action — and discovered that two of New York’s biggest insurance providers may have scammed roughly $1 billion out of taxpayers, a newly unsealed lawsuit charges.

Kami Barker brought the whistleblower case against Empire Blue Cross-Blue Shield and its partner Emblem Health under the state’s False Claims Act, which provides incentives to citizens who expose fraud — offering up to 30 percent of any payout.

The 37-year-old Emory Law grad says she was shocked when the insurers stuck her with a roughly $260,000 bill for medical expenses tied to four hospitalizations between February 2012 and November 2013.

Barker, then an attorney for the city Law Department, visited in-network hospitals while battling trigeminal neuralgia, a chronic pain condition that led to recurring septic infections. The illness was unrelated to her disability. She’s been in a wheelchair since age 11.

When Empire — which covers 600,000 city employees, retirees and their families — left her holding the bag for such a huge cut of the total $1.26 million in care, she became suspicious.

“So my room and board was paid for but my doctors were not, my surgical procedures were not, and my medicine was not,” Barker told The Post on Tuesday. “That’s how I ended up getting footed with all these bills.”

After some digging with the help of attorney Steve Cohen she discovered the insurer “deliberately exaggerated the benefits available under the plan, while understating the uncovered costs that must be paid by members,” her suit in state Supreme Court in Manhattan says.

For example, a summary of Barker’s plan said that if she chose in-network hospitals she “will save money.”

What the material didn’t disclose was that many of the doctors working within those hospitals were out-of-network.

Of Barker’s total $1.26 million in claims, Empire and Emblem only paid the hospitals and doctors a combined $625,000.

Barker was stuck with $13,000 in deductibles and copays, $164,000 for out-of-network costs, $47,000 for denied claims, and $32,000 for lost claims.

Barker and Cohen also claim in the suit that Emblem “engaged in old-fashioned accounting fraud to overcharge the city for insurance services.”

Every year the insurers submit 50-page reports showing how much they paid out in claims.

What Barker and Cohen noticed is that the report’s profit and loss statement showed one figure — for example, in 2014, $1.31 billion for claims — while buried on another page among some 400 other figures was a different number: $1.23 billion for claims in the same year.

Barker alleges the insurers only paid out the lower figure — $1.23 billion — while charging the city higher premiums based on the larger payout amount.

“There’s an absolute accounting discrepancy that’s never been explained,” Cohen said.

The insurers inflated the payout amounts by an average of $55 million each year between 2008 and 2014, the suit alleges.

Emblem also “billed the city for sales and marketing expenses that did not occur,” according to the complaint.

It charged the city $19 million in 2013 for marketing despite having no major advertising campaigns that year, the suit says.

Meanwhile, Empire promised to reimburse members at a rate of 80 percent for out-of-network costs.

But a study found that in 2014 average out-of-network procedures came to $2,118 while members were paid only $614 — or a rate of about 30 percent.

“This failure to reimburse at the promised rate costs plan members millions of dollars,” the suit says.

Barker’s suit seeks $1 billion in reimbursement to the city and state and another $2 billion to taxpayers as a punishment to the insurer.

In a similar New York False Claims Act case, the British pharmaceutical company GlaxoSmithKline paid $3 billion in fines in 2012 for false advertising about its popular antidepressants.

And this is not the first time Emblem’s operations have been accused of dubious dealings. In 2014 a subsidiary of the insurer had to create a $3.5 million consumer assistance fund and pay $300,000 in penalties to the state attorney general for allegedly denying members millions in reimbursements.

So far, state Attorney General Eric Schneiderman has declined to intervene in Barker’s suit on behalf of New York taxpayers, but his spokeswoman told The Post, “We’re continuing to monitor the case.”

An Emblem spokeswoman called Barker’s allegations “completely false.”

Empire Blue Cross did not return messages seeking comment.