Unacceptable service from MTN

I have had many problems with my Samsung A7 and very bad service from MTN and the new phones I’ve received are still giving me problems. I went to Howick to upgrade my contract on the 16/11/2015 to a Samsung A7. From the second day I had it the phone would randomly restart in the middle of a call or just during the day. Within the first week the phone screen would not turn on, only the 2 buttons at the bottom would light up. Since it had not been 7 days they said they would give me a brand new phone. This took me 2 weeks to finally get and instead of getting it from Howick I had to phone and go to Cascades otherwise it would have taken longer but I had to discuss and make this plan. The second Samsung A7 lasted 4 months. I left it off charge for the night and when I woke up I put it on charge and it wouldn't charge. I sent it in back to Howick MTN and they said they will need to get it sent in which will take 14 days. a Month later I got a call that they’re replacing it. I get to Howick to tell me that they were broken into and all phones were ****** so I only got it the following week. The new Samsung A7 I have now restarts between 5-15 times a day and almost every time in the middle of a call. I am very disappointed with the Samsung A7 and MTN’s service, this whole thing is just completely unacceptable, and even though the phone has a 2 year warranty it's clearly an inferior phone and will just continue malfunctioning. The 30gig promotion MTN had was barely used as I was waiting for a new phone and I have paid for this contract and handset for 2 months that I did not have it. MTN’s communication is terrible and they can absolutely not stick to the time limitation they have set themselves (14 days) and made absolutely no effort to keep good customer service.