Warranty rejected twice of faulty device

I've had a terrible experience with a samsung S7 (Seriel No ********** ********** 9), (Job Card No: ALWIC ********** ) the phone was overheating and rapidly draining battery and I took it in for a warranty claim, I was told the warranty had been declined because of a scratch on the home button.

The said scratch was barely visible, and besides I was told the phone had a current fault on the electronic board and it had to be replaced. (To this day I still don't get what a negligible scratch on the home button has to do with the phone's electronic board, unless I really need electronic lessons for dummies. ) Needless to say its been two months after the repair and now the phone is no longer vibrating and MTN has rejected the warranty claim again. I have no idea what mindless person makes a decision to decline a warranty claim on a phone that is clearly faulty. I mean the phone has been brought to you twice because its faulty, wake up mtn and deal with this.

Sindi