Laws on a company buying and collecting a consumers store credit card debit that was purchased from the compa?

consumers rights on outstanding debit to a store (Mervyn`s) that is no longer in buissness that has sold there customers credit card debit to another company ( Law office of Budzik & Dynia LLC) that is trying to collect the outstanding debit and is threatning legal action if not paid. i live in california and the cmpany that is trying to collect is in chicago Il