BRAND NEW UPGRADE PHONE NOT WORKING!!!

I've upgraded my phone on the 11th of November 2015, they delivered the phone at my office on the 26th of November. I took the phone out of the box, inserted the sim card and it kept on losing signal. I went to the MTN store in the East Rand Mall, (Gavin Smith) 2IC of the store examined the phone and it keeps dropping signal it stays on for 20 seconds(he even wrote a letter stating that the device is not working). The 30th of November I phoned MTN the guy logged an e-mail to Vusi (the guy that did the upgrade), so that he can get them to come and collect the phone, I haven't heard of him AT ALLLL. I called in that week again and again, and NO ONE CAN ASSIST ME!!!!!I went back to the MTN store in the East Rand Mall on the 12th of December 2015 , spoke to Gavin Smith again, he contacted MTN for me and then I spoke to Prins, he took al my details to arrange the collection in that week, he told me that they will come and collect the phone in that week and then I will receive it back the following week before I go on holiday. I havn't heard from ANYONE at ALLLLLL! I've paid 2 debit orders already and NO ONE IS HELPING ME. The contract number is ***, please call on ***