Telkom debit order still running after a year of cancelling the service.

I have cancelled my service with Telkom in March 2020. After many phone calls and emails, they eventually disconnected the line. Their debit order, however, still goes through my bank on a monthly basis. I have requested a refund, at this stage around R10,000, but to no avail. I have requested my bank to stop the debit order. However, Telkom just changed the amount of the debit order, and claimed it twice in one month. They have also handed me over to a collection agency, claiming my account is in arrears. That is for an account that should not exist anymore and that was still paid on a monthly basis???!!!