Blacklisted by Telkom for a contract I do not have with them.

A year ago I concluded a contract with Telkom. When it was clear that they did not cover the area I lived in, the contract was canceled and I received a cancellation confirmation. The phones were handed back and that should have been the end. Alas, I walked into an admin nightmare, was billed every month and had to stop payments month after month. I kept sending them my cancellation codes and after nearly a year they were able to resolve the problem and the debit orders stopped. I thought that was the end of my problems, until I wanted to enter into another mobile contract, only to find out that Telkom had blacklisted me for non payment of a service I could not use on a contract that does not exist.