Account keep pilling although I have cancelled the contract.

Ever since I agreed to the contract with Telkom, I have never received any joy. First they were over charging me and I always had to go to the branch or to call, at my own expense for them to fix their mistakes. I ended up stopping the debit order and opted to pay manually. Which I did. When the time for me to cancel the contract came, I called and I was told that my account has been suspended. I then told them I don't car about the line as my son has lost the tablet and he doesn't use the number no more. They then said I must send proof payment, which I did. Guess what? The account kept going up and up and as usual, I called them again to query that. I was told the manager will call me back. Until today my account hasn't been sorted, and it's hitting sky high. Worst part they have now backlisted me and I can't get credit anywhere because of them. Yet I'm still waiting for the call from the manager. I don't know what's happening just that I have been listed. Please help me