Very bad service received from MTN concerning phon

I've had a phone which went in for repairs last October. It has been going back & forth between me & the repair center, they say they can't pick up the problem. They even tried excuses of the charger I was using. Every time I have to contact them & no one ever gets back to me. When I inquired yesterday with Smart Phone plus, I was told they have my phone & don't know what to do with it. The Insurance department says I should take the phone to any authorized repair center, of which they can't tell me of any. Why should it be my responsibility if I pay insurance every month.