Norman Bissett & Associates Group is not helping

My TFG account has been sold to Norman Bissett & Associates Group in 2018 and I made arrangement with them, settle the account. the paid up letter was send to me in 2018. since 2019 when I apply for credit with TFG group am told that am still owning the account. when I ask Norman Bissett & Associates Group they say they have send the paid up letter to TFG yet TFG is saying am owning I did try my best to solve this issue, since 2019 till to date. is been 5 years now paid the account but still the shop has not cleared my name because Norman Bissett & Associates Group is not helping yet I paid them.