Worst service from MTN

My phone has been in that repair store 6 times, for the same problem. They claim to have replaced the electrical parts and this is for the 2nd time but still the phone comes back with the same problem. How and why? If they replaced the parts. The phone switches on and off on it's on. The phone has been with man repair since January till today, I only get it for a day then I have to re book it again. I'm tired when it's about this phone because even the mtn head office knows about this issue but I still have to spend more money and time due to this phone which I'm not even using for the past 6 months. Very disappointed with mtn because as long as they get their money from your acc they don't even care about the service they give the customers. I don't think the head office even cares at all.