To be 100% honest, you dont have to pay any collection agency, your account is with the bank, and if they sell that account they must notify you in writing of the sale of it and if you consent. No one ever see's these and dont know the real legalities behind them.
I am currently in court sueing my bank, a few credit card companies and gmac for fraud.
So far I am in favor of winning, they dont even know their own small print.