MTN should review its customer service urgently

This company does not deserve even one star. I am utterly desperate. I upgraded my iPhone in June of this year in response to a call purportedly from MTN. It transpired it was actually a third party working on behalf of MTN. The contract was emailed to me and the phone duly delivered several days later. Two weeks into the contract the phone stopped working. I took it into the MTN Sandton store who sent it to their repairs dept. and two weeks later notified me that I should call the MTN helpline to arrange a replacement phone. I have phoned MTN at least 20 times, being passed from one person to another and eventually being told I have to cancel the contract, which will take at least six weeks and then start from the beginning. It is now at least six weeks later and am still paying the contract that includes a phone which I don't have. The person at MTN Sandton told me that some customers have waiting for a year to resolve similar problems and advised me to call the third party to resolve it. I have just done that and was cut off after explaining the problem. Any suggestions?