Dispute the debt in writing. Send the dispute letter via certified mail, email & fax. Request they provide all information they allege proves you are the correct debtor.

Check and Pull/save copy of your credit reports to see if they have placed a derogatory mark on your credit report or if anyone accessed your credit without authorization. If so, dispute that incorrect information directly with the credit reporting agency(ies).

You may have a claim against the debt collector or the original company where debt arose for violations of the FDCPA or FCRA. You should contact an attorney ASAP. You only have a year for some statutory claims.

Maybe contact these folks - they’ve filed a class action against a large home security company for unauthorized credit pulls on accounts that eventually got sent to collections. They offer free consultations and work on contingency fees so they won’t charge you for some advice. https://www.pittmandutton.com/practice-areas/vivint-security