Paid in full but blacklisted!!!

I paid off Avon on the 085/12/2017 and sent them a proof of payment, then asked them to send me a paid up letter and remove my name on the ICT. On the 10/01/18 they confirmed that my account has been paid in full and i only received the paid up letter on the 14/02/18 after asking for it continuously. I have since repeatedly asked them to remove my name from the ICT as they have blacklisted me and they still haven't!! This is creating problems with my credit score. I regret the day that i started selling this product and i want my name removed ASAP before i take further action!!!!