Telkom contract cancelation

I had a 24 month wifi contract with Telkom which has served me well during the period however around month 22 my internet was stopped. When I called to query this I was informed that the contract has ended. This was around May. I then proceeded to have the contract canceled and in turn switched my service provider. Telkom has provided me with interest since May but have attempted to debit my account for services not rendered. When I queried this they cannot provide me with feasible explanation as to why my request hasn't yet been granted. In addition to the above, I'm spent a lot if money trying to get in touch with Telkom which is a problem in itself. The service I've received from Telkom is appalling. I've spoken with another colleagues who's been experiencing the same issues when trying to cancel their contract, which appears to be a known issue. I'm not happy that I've requested to have this contract canceled on several occasions but this has not been processed after I've received telephone confirmation that it will be done. Off the back on that Telkom is still attempting to collected funds when I haven't been using their services. All I want is for the contract to be canceled and no further collection attempts done on my bank account.

How do I go about getting my request granted?

Please help!