Lack of service and Ethics

Since Oct 2018, I have had no service from Telkom but I am still being charged monthly. All emails phone calls, visits to Telkom (Musgrave) have yielded no results. I have been promised a credit once the problem is resolved. IOW once I receive the wireless handset - am told over and over, that they are out of stock. what do I do, as any credit owing to me will be lost once I cancel. I believe that is another horror story !