Unacceptable service coupled with misrepresentation

I upgraded my contract on Friday 01 September 2017 at the MTN franchise in Fourways and purchased a new iPhone 7plus 128GB. Part of the terms explained to me was that should the phone give me problems within a 7-day period I should be able to return it to the store and get a new phone instantly. The very next day (Saturday) I realised that the phone was not charging. I tried multiple chargers and it still refused to charge. I returned the phone the next Friday to have it replaced since it still fell within the 7-day period. I took the phone back to the Fourways MTN shop I bought the phone from and I was told that they do not have stock of the iPhone 7plus 128GB. I was told that on Saturday they will check to see if other MTN stores have stock of the phone to order from them. I did not receive any feedback from them on Saturday. Monday I called the store to find out what the status is, I am now being told that I have to wait for a warranty assessment and only then will I get a phone. I called back for an update on Tuesday I am being told the phone has not been collected for an assessment. I have already spent 4 days (as of Tuesday 12/09 and counting) without a phone which I am paying for. Next thing the promise that was made by the sales consultant (Luhle) that I will get a new replacement phone same day if there are any problems identified with the device within a 7-day period was not kept. I am utterly disappointed with the service I am receiving from the MTN franchise in Fourways, more than that I am annoyed at the fact they misrepresented themselves with the 7-day return policy which is not being app****.