Fees not owed

Last year my Woolworths account was handed over to RL Daly attorneys. I paid up the account and received the paid up letter from them. Now mbd is saying I owe them for the same account. I called into the call centre and they tell me that although the account is paid I owe them legal fees. How do I owe legal fees on account paid through RL Daly which was paid before mbd got involved.