A Minnesota debt buyer accused of charging people as much as 22 percent in bogus interest on old bank overdrafts and fees is the latest target in the state’s crackdown on illegal debt collections.

State Attorney General Lori Swanson on Wednesday sued Bradstreet & Associates LLC, claiming the Plymouth-based collections agency added illegal interest on old debts that Wells Fargo & Co. and U.S. Bancorp had written off and sold. Much of the customer overdraft debt is bank fees, Swanson’s office said.

Bradstreet and its predecessor bought $18 million of charged-off balances from the two banks since 2009, then routinely filed lawsuits against consumers across the state, according to the complaint. Swanson said 16,000 Minnesotans were affected by the collectors’ practices.

In the case of a young Willmar woman, five years of illegal interest caused a debt of $1,886.20 to balloon to $4,108.72.

“You can see how the small amount of money can quickly spiral into these outrageous amounts of money,” Swanson said in an interview. “The scope of this one is significant. In this case it’s a wholesale imposition of the wrong amount of money.”

Bradstreet has offices in Plymouth and in Edina’s Southdale Center, and was formed in 2010 by Mark Roering. Neither Roering nor the company responded to several requests for comment Wednesday.

The high interest rates charged by Bradstreet are well above the state’s interest-rate cap on such debt of 6 percent. The contracts that consumers had with the two banks didn’t authorize any interest to be charged on the checking account overdrafts or related fees.

Jennifer Brummer, a Minneapolis mental health therapist who works with veterans, said her ordeal with the collector began with an unresolved dispute with U.S. Bank years ago over $250 in overdraft fees. Fees pushed the debt to $2,073.11, she said. After the bank charged it off, the bill wound up with Bradstreet, and the balance surged to $4,311.74.

Brummer said she paid Bradstreet a total of $1,700, sending monthly payments of $100 from her checking account. But she filed complaints after collectors repeatedly called her at night and at work and telephoned her parents too, she said, adding that Bradstreet refused to give her proof of her payments or validation of the debt.

“I feel sick about it,” Brummer said in an interview. “They threatened and called me a scumbag that didn’t pay my bills. I really wanted to speak out for the voices of the unheard.”

The lawsuit, filed in Hennepin County District Court, seeks a stop to Bradstreet’s practices and restitution for consumers.

Mark Schiffman, spokesman for the Minneapolis-based ACA International, a trade association representing debt collectors and debt buyers, said Bradstreet is not a member. He called the legal actions against debt buyers and collectors “hugely concerning,” but that companies need to play by the rules.

“The vast majority of our folks are trying to do things the right way,” Schiffman said. “There’s always going to be outliers, bad apples.”

According to the complaint, Bradstreet bought the old checking account debts from United Credit Recovery LLC, a Florida debt buyer that the attorney general sued in October for churning out fake bank affidavits on a “mass scale.” United Credit Recovery was allegedly cutting and pasting bogus signatures of bank officials onto the documents to make them look authentic.

In July, the attorney general and state Commerce Commissioner Mike Rothman sued California-based CashCall Inc. in what they described as an Internet-based “rent-a-tribe” scheme.

They accused CashCall and its subsidiaries of charging illegally high interest rates while fraudulently claiming the loans are subject to tribal sovereign immunity because they’re made by a South Dakota company called Western Sky Financial Inc. that is owned by a member of an American Indian tribe.

Minnesota passed a law last year that, among other things, requires debt collectors seeking default judgments in court to show evidence they have the right person and an actual debt, and sets a six-year limit on debts that can be collected.

The state’s efforts reflect a national push to clean up the multibillion-dollar debt collection industry that flourished in the wake of the housing collapse and recession.

The Consumer Financial Protection Bureau is considering broad, new debt collection rules that could encompass banks collecting their own debts owed to them. The watchdog agency started accepting consumer complaints about debt collectors in July as part of its giant consumer complaints database.

U.S. Bank and Wells Fargo have said they no longer sell off account overdraft debt to collectors.