Regret the day I joined

I regret the day I decided to join MTN, I took out an IPhone on Contract after a few months, the phone started giving problems, the speaker and the charging port wasn't working properly, booked it n for repairs since it was still under warranty, after a month we received a bill of over R7000 to fix the iPhone, no one could give me a reason as to how the amount got to R7000 and some change, people at MTN Clearwater was clueless and every time I went to query they said they don't know anything that's happening at the repair center they will get someone to contact me with an answer, but as usual no one phoned me, I ended up phoning repair center asking about the R7000 invoice, they said they will investigate and let me know why it came to R7000, yes you guessed it no one ever contacted me. After 3 months of my phone lying in the repair (booked it in December) center I get a message saying my phone is ready for collection, after collecting my phone nothing was fixed and I'm still no closer to getting an explanation for the R7000 repair bill, I need this phone fixed, I am fuming, why sell someone an IPhone and then after it starts giving problems everyone pretends to know nothing, for R7000 I can almost buy a brand new IPhone, mind you it's still under warranty so this needs to be fixed, I am tired of MTN and their ****** excuses and incompetence and lack of customer service