The Federal Trade Commission gets more complaints about debt collectors than any other industry, with consumers claiming that they’re being hounded for debts they don’t owe or for the wrong amount of money.

In the first study of its kind, released on January 30, the FTC examined data on debt buyers, looking at more than 5,000 portfolios containing nearly 90 million consumer accounts with a face value of $143 billion. Creditors often sell debt that they have not collected to such buyers.