Telkom Cancellation of landline

Worst ever experience dealing with Telkom. We cancelled our line in 2017 as per advise given by Telkom employees in CC. We also went to a Telkom shop to cancel our line. Got a mail from Telkom's collections department 7x months later to pay our account. Lady didn't even worry to try and assist. The response was just I am not working in that department. Next we got calls from debt Collectors and this is where the nightmare started. They are arrogant and don't listen. The more we are trying to explain the less they want to listen. We have send them emails as well without them acknowledging that they received all our documents. You cannot call them they don't answer there phones.

How do we stop this nightmare?