I didn't sign a contract with the debt collection agency do I have to pay them?

If they bought the debt legally and they can produce the contract you signed with the original creditor, than that's what's called validating your debt. If they are pursuing you you have a couple of options. 1. you can send them a C&D and @. you can request that they validate the debt, that is usually done within 30 days of them initially contacting you.