ST. PAUL, Minn. (WCCO) – Minnesota Attorney General Lori Swanson says a federal investigation is needed to look into business practices at one of the nation’s largest private Medicare insurers.

On Friday, Swanson sent a massive file of complaints against Humana to the federal agency charged with overseeing that part of Medicare.

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She’s asking the Centers for Medicare & Medicaid Services (CMS) to look into more than 27 complaints on file.

For the past couple of years, Humana policy holders in Minnesota have complained of improper denial of coverage, overcharges for co-payments and failure to follow the required appeals process.

Kentucky-based Humana provides private Medicare insurance coverage to more than 100,000 Minnesota seniors.

This investigation into Humana’s alleged wrongdoing has been going on for a couple of years, Swanson asserts. It stems from both consumer and medical provider complaints from across the state.

At 75, Darlene Tucker lives on a social security check totaling just $1,200 a month, which is why she purchased a Humana Medicare Advantage policy several years ago to insure that she would have full medical coverage, without costly co-pays.

But Tucker can’t think about her experience with Humana without becoming upset.

“Very angry, but it makes me cry when I think of it,” Tucker said.

She had breast cancer and endured 32 radiation treatments. Each time she had a treatment, she was charged a $25 co-pay which ended up totaling nearly $1,000.

It was a charge that her policy was supposed to excuse. When she got the bill, she couldn’t believe her eyes.

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“I didn’t have it, I’m on Social Security so that amount, I just about started crying,” she said. “It still bothers me.”

Within months, the bill was turned over to a collection agency which was demanding payment.

But Darlene Tucker is not alone. The Minnesota Attorney General’s office has gathered sworn affidavits from 27 Humana policy holders and medical providers – each one complaining of the company’s business practices.

“One problem we’ve seen is Humana denying coverage for things that Medicare would clearly cover,” Attorney General Lori Swanson said.

On Friday, Swanson sent a letter containing all 27 affidavits to the federal administrator for the Centers for Medicare & Medicaid Services, the agency responsible for regulating private Medicare insurers. Swanson wants CMS to investigate the allegations – from improper co-pays to its handling of claim appeals.

“Whether it’s a $50 co-pay or a $5,000 medical bill, it matters. We just want them to hold true to what they promise people,” she said.

Darlene Tucker has since changed her private Medicare coverage to another company. But she is still bothered by the whole experience.

“It makes me feel bad that others had to go through it too,” Tucker said.

Humana was contacted for comment on the allegations, but a company spokesperson said they haven’t seen Swanson’s letter.

Humana spokesperson Kate Marx says they take these situations “very seriously.”

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“We have been successfully serving the people of Minnesota for more than 10 years, and more than 100,000 Minnesotans belong to Humana plans. Our Minnesota Medicare Advantage plans have achieved one of the highest CMS ratings for performance and service, with a rating of 4.5 stars on a five-star scale,” Marx said.