Money gone, but still reflecting as unpaid on ITC. *******s

I had an account with Jet which was handed over to them, they sent me a paid up letter which I was told I need to send to JET so that they can clear my name from the Transunion. Jet unfortunately does not have my details anymore as I do not apprear in their books any more because my account was handed over. Now I have to be the one to chase after them to send get this letter to Transunion. When I was paying off the account I was never told I would have to then fight for this account to be cleared on ITC, have I had known I was not going to waste my money and pay an account only to be reflected as still owing years after paying. Daly Credit Corporation were kind when they wanted my money now that they have taken my money they are unable to assist me.