Still being billed for account cancelled in January

I cancelled my Telkom ADSL line in January 2017 at the Telkom Cresta store. I then discovered months later that I was still being billed for this and that it was now affecting my credit report. I have since been back into the same branch and completed the cancellation form again while also speaking to a lady in the accounts department who said the matter would be reversed and that I would be having the amount reflecting on the account credited and any negative record on my ITC would be cleared. However, I have today found that not only has this not happened but that the amount due has increased.... This is totally unacceptable. What must I do to get you to just do your jobs and stop being so damned pathetic???? I want this resolved with immediate effect which includes the credit as well as the clearing on my ITC. Response required!!!!!!