Still Being billed after cancelled in March 2015

I had cancelled my contract on the 12 of March 2015 ref ***A( reason for cancellation as our wifi had never worked. EVER), 3 months later I'm still being billed and say I am behind and threats are being made that they will hand me over. The 13th of May 2015 ref ***6, I had called and they said they will fix it and pass the credits, still TODAY, I have been sent a new bill dating all previous months had not been paid and they will had me over. On the 13th of May I had to hold for 2hours to get it sorted again. This is the worst service I had ever experience. I want this account to be sorted coz it looks like calling your call centre does not work. Telkom is quick to take your money, for services that had never worked and then if you cancel you are still being billed.