Scam. Typical phrase of the debt scammer. Somehow or another a "check fraud" matter came to their attention. Which is total clap-trap. Check fraud is a crime. If you had committed that crime, or were suspected of commuting it, you'd be interviewed by members of law enforcement on a face-to-face basis. You would NOT have heard about this from some scammery-scummery debt collector who cold calls you and starts demanding money. Because that's what will happen if you call them back. Debt collectors have nothing to do with bad checks. And they have no influence on law enforcement. Ignore and block this call.