MTN do not honour contract

I got a new phone in March. The bluetooth in the car did not work. They exchanged the phone (samsung J5 prime) for the same phone. The problem was the same. They sent the second phone to samsung in early August. It came back, the problem persisted. They sent the phone back on about the 4th September. I have not heard a word, although I am still paying for the contract. I went to the store late in September on a sunday, they said they could not help me because it was a Sunday but would contact me. That was over 3 weeks ago. I sent a complaint to MTN about two weeks ago. They have not even acknowledged receipt thereof. I am disgusted with their lack of concern for a customer.