REGRET SIGNING UP WITH THESE THINGS

I am disgusted to say the least , I called for a road side assistance as it is part of the package on Imax3. I regret the day I called these people. When I was contacted by a towing company , they told me they are coming 96km away and I was 10km before the next town. I then canceled with the towing company and still spoke to the consultant who was assisting me. Weeks later I get an invoice from them for a service I never used. I called the accounts department and explained, the rude , clueless agent told me that I will have to pay it cause it was never canceled on their side. . I refused. They continued debiting my account after several mails and phone calls with no response. Today only I called them over 15 times , no answer as always. I continue getting threatening sms and emails from them , I reply to them mails attaching unanswered queries from my side but they just ignore. Now I am handed over for an invoice I refuse to pay. I have been reversing the debits hoping they will call me but it's just mails and smses. . I am frustrated, I want to purchase a vehicle but I am told Matrix handed me over. . I now want to pay that money so as not to ruin my credit score but I can't get hold of them. .