From good to bad service

Cell c does not respond to my requests. I has a contract with them since 2011. I paid it finished in January 2024. Informing them in the email, that I want my number prepaid, as my contract is done and paid up. Now I have a listing on the bureau with an amount that I am not liable for and did not make use of the service. I have contacted them many times. They don't return my calls. I want this sorted out and my name cleared by the bureau. I even considered paying just to get this off me..... But why should I pay for a service I didn't use and then the number was blocked and disconnected.