Tired of dealing with useless call centre agents

I had a sim only data contract with Cell C which ended and thereafter I converted it to prepaid, in late 2014/early 2015. This contract still reflects on my credit report as active, which is negatively affecting my score. I contacted Cell C to verify that I do not have any contracts/lines with them. They confirmed (after being transferred from agent to agent). I asked for a letter confirming this, and was put through to the legal department. The line just rings with no one answering. It's highly frustrating that no one at the call centre can be of any assistance. Please can some higher powers within your company get a responsible and well trained employee to issue me with a letter confirming that I do not have an account/contract/lines with you and I am not a customer of Cell C's! (This is the main reason why I converted the sim to prepaid and will never take up a contract with you guys again - the pathetic service). PLEASE NOTE, THE CONTACT NO. PROVIDED HERE HAS ABSOLUTELY NO DEALINGS OR ASSOCIATION WITH THE CONTRACT IN QUESTION. THIS IS JUST A NO. FOR YOU TO CONTACT ME ON - I am stating this as previously an idiot from your call centre messed up everything due to this.