Poor service

I upgraded my contract on the 19 October 2015 via telephone with Joshua. I received the phone on the 22 October. on the 25 October the phone just switched off and could on go back on. on the 26th the phone went back on but it would no longer vibrate. I e-mailed Joshua advised him that the phone is giving me problems and I will be returning it to the store. I went to Mtn in Rosebank mall where they advised me that I should call the call centre and report this so they can collect it. on the same day I called the call centre they advised me that Joshua is the only who can assist me as he was the one who did the upgrade.I called again on the 27th when I spoke to Lorraine (ref ***) she told me the same thing and she will ask Joshua to call me on the 28th Joshua then sent me an e-mail saying they will collect the phone on the 2 November I called again and spoke to Gregory (ref ***)he advised me that he will e-mail Joshua and ask him to give me a call which also never happened. on the 3th November I called again and this time I spoke to Musa ref ***7 said Joshua will call me. which he did again saying he will collect it. To date I still have a faulty phone.