i phone not repaired after fourth time!!

My i phone 6S was sent in for repairs after i only had it for four months. It was sent in on 2015-09-10 it came back with only one problem fixed. sent in again on 2015-10-20 - came back again with only one problem fixed. Sent it in on 2015-11-11 - came back not fixed took it back after 5 hours. Received sms on 2015-12-18 that FMI was on (after i watched the lady at mtn put it off when i booked it in). MTN service provider checked on their computer and it showed FMI was off. never the less i had to pay R330 for HVRC to look at it again. Fetched it on 2016-02-17 and it didnt even want to switch on!!!! MTN suggested a flat battery so i charged it at home with 3 different chargers but it still dont want to come on!