VVM harassment by call centre staff when they do nothing themselves

I have been harassed for months about a telkom account. I cancelled the account in November 2017 and Telkom despite acknowledging my cancellation notice have continued to bill me up until February this year. I have sent in all documents and received a reference number from VVM but they phone either me or my wife who is the account holder at least twice a day about this. They have not done anything to resolve the issue using the data and documents sent but continue to harass us and i am getting sick and tired of this. I went onto their website and tried to contact a senior manager on their chat line but the system does not respond at all and is useless. Why offer this if it is not monitored