They telling me I own them money.

My account was handed over, a while back by Truworths for being a bad debt. I slowly started paying my account at truworths. In June 2015 I settled the outstanding amount in full. A month later I was called by creditworx telling me I owe them money. <br> I spoke to truworths and they have assured me there is no such, and gave me a settlement letter. This company is mistreating me with calls everyday and trying to milk money from me, and Im sick of it. I don't understand why I will owe money to them whilst I only had an account with trouworths.