Faulty Phone - MTN giving out faulty phones on contract.

I am logging this on behalf of my mother, who has taken up a contract with MTN. My mom took up a phone contract (Samsung) last year, ever since she has had the phone its always been bothersome and has been taken in for repairs 4 / 5 times already. what is highly upsetting is that my mother is paying for a phone that is not working and the MTN in PE (Gqeberha) are giving her a run around and not giving her a new phone or cancelling the contract, as the phone is faulty. She once again took the phone in for these random repairs and its been with MTN for about 3 weeks now and no one is bothering on giving her updates on the status of the phone. I would appreciate if someone with scruples to contact her with a solution to the problem as the phone in question is faulty and I do not see how MTN does not give her a new phone as she is paying for a phone that is not working.