New phone repairs

i purchased a Sony Xpeira Z3 compact on contract on the 27/10/2015. Everything was fine and then on the 15/11/2015 it switched off and every time I switched it back on again it would restart itself. I took it to the bluff MTN branch and they couldn't assist, and would send the phone away to be looked at and advised it would take 3 - 5 working days for me to get my phone back. On 17/11/2015 I went back to the Bluff shop to do a follow up the lady was very unprofessional she didn't ask me for any of my details. I wrote down my alternate contact number on a piece of paper she took it and marked it for someone else's attention to deal with . I then asked if she knew which phone it was for and only then did she ask me for all my information as she was assuming all along I was some other customer coming in for feedback, and then advising me that it would take up to 5 weeks for me to get my phone back. The consultant also added that my phone was still sitting in the shop and had not been collected by the courier company. I fail to understand why I now need to be inconvieniced for the faulty phone given to me. if that's the case then MTN needs to replace my phone with a new one.