Cancel the contract if you're failing to fix the phone. I'm tired

Had to take back my Redmi to MTN for the 3rd time now because of the same problem I was told twice already that it's fixed. For 3 months I didn't have a phone. They said they were fixing it. Each time they send it back to me it still has the same overheating problem. I have been paying for a phone that is with them. No one ever called me after I complained the first time. I guess they will ignore this review as well. I regret ever taking a contract with MTN. No one seems to care.