non cancellation of service for a years

I had two 8ta contracts for about 10 years with telkom. In January 2017 I gave notice to cancel one expiring end of January the other expired in December 2016. I sent in the cancellation form to telkom. they continued to bill me I telephoned them and repeated the cancellation I went into telkom in Table view and handed in the cancellation. They still continue to bill me. I called monthly and visited a telkom office in Tableview again in June and they then cancelled one of the lines and didnt back date it to January. They have continued to charge me for the other service monthly for a year now insp[it of 11 phone calls and 3 visists to the telkom branch in Tableview. They have now handed me over for collection and black listed me!!! On top of that inspite of my constantly calling them to correct there error they have NEVER contacted me even once and hand me over without even one attempt to call me and sort there problem out.