Faulty merchandise and incompetence

Within first week of getting my upgrade iPhone i was unable for 2 days to take calls because it said headphones were connected although there were not. I went to MTN Constantia for help and they turned me away saying I had to pay R350 to send it away! This happened on and off for the next few months but because of busy schedule I had to deal with it because I knew MTN were as unhelpful as could be! Then my phone stopped charging. I took it to the mtn shop in constantia and they said it was the charger so spent R300 on a new one. Got home and same problem. To the point where my phone died and was Unchargeable. I took it to mtn westlake. They sent it for repairs on 29/12. I heard 2 weeks later that they couldn't work on it until find my iPhone was disabled which I did. I then heard back another 2 weeks later and they said it still had not been disabled. But it has been! I did it! I went into mtn westlake today to find out what the hek is going on and they have no idea! They are now saying that I must pay R350 before they can look at it but they can't because iPhone find is still on. What ON EARTH IS GOING ON! WHAT DO I NEED TO DO TO GET THIS SORTED CLEARLY THE PHONE IS A DUD!