RETURNED SONY EXPREIA M5 CLAIM REJECTED

On the 08th of February 2016 returned a Sony M5 Experia which I had received/bought on the 28th of December 2015. The battery is faulty, phone switches of at 88% full battery capacity. I have to connect phone to charger to switch it on. The phone was dropped off at Nelspruit Riverside Mall. I was told to call the repair centre in the third week. I did call on the 01st of March, held the line for 10minutes and was told my phone was not booked for repairs. I must go to Riverside and check if they did send the phone. On the 05th of March I went to Riverside to enquire and they said the phone was received back from repairs and claim is rejected. I have to go to MTN Head Office where I bought the phone so that they can lodge a claim and exchange the phone. The reason it was returned is MTN fear stock loss so the return must be done at the place/shop I got the phone. They gave me back the phone together with invoice which they said I will need and advised that I go to Johannesburg Head Office. I need MTN to deal with this matter and give me a working phone.