New iPhone 6 - handset problem not replaced

I signed up for a new contract with MTN - my service provider and got a new iPhone 6. There were problems with the phone - returned handset - waited 5 days and got it back with MTN stating there were no problems. I could not download anything from APP store. I took the phone to digicape who wrote a report confirming problem with handset. Went back to MTN they refused to acknowledge. the staff attitude at the V&A shop was dreadful - no compassion - \could not care less"attitude. I went to the iphone shop in V&A who ALSO confirmed handset problem. I now had 2 reports. Went back to MTN who still refused to replace handset. The phone was taken in and sent back to their technicians. They told me they would escalate it and I would hear back the following Tuesday (I returned the phone on Friday). I have subsequently not heard from them - they do not reply to emails - and I CONTINUE TO PAY FOR A PHONE THAT I DO NOT HAVE. I am appalled at the shocking service"