Bad service

In February I requested settlement for all my accounts and received only 3 and I paid those 3 and got settlement letters. A week later I was contacted that I have a cell c account which wasn't sent to me, since then I've requested that the account be closed as I don't owe cell c any amount and they keep asking for proof which I can't provide and cell c isn't willing to assist also. I have no intentions of taking another loan to pay 9ff this account and my request to close it with Nimble is failing coz I don't get response from them.