Unhelpful staff bad service

I took a Sony M5 on contract with MTN in late NOV 2015. The phone was giving me problems thru out, I decided to take it back to the store on the 02 Feb 2016 and I was told that phone was recalled and that they first need to take it for assessment before I get another phone. Its four weeks now in still without a phone, after several calls I was given a ref number to go to the store an d get another phone, when I thought my misery was over I was then told that they can't give me a phone I need to call MTN door to door to assist seeing I did my upgrade with them. When calling them I'm always told stories. Can someone please assists and let me know if you can't help , so I can go and get another phone with CellC or Voda.