Pathetic service from MTN!!!

I bought a new Sony Xperia Z from MTN in December 2013, in December 2014 i was on a call and it cut off, the phone switched off, and wouldn't switch on again. A few hours later it switched back on but this time in safe mode. I tried the hard reset, soft reset and factory reset but to no avail. I took the phone in to the La Lucia branch on the 13th of Jan and was told it would take 10 days to get the phone back, but they would keep in contact with me, after 10 days I still heard nothing so I went in only to be told that the Sony products take 15 working days, still I heard nothing from them. I went in again and was told they had been trying to contact me yet I had no missed calls or voice mails or anything. I was told the phone repair would cost more then the phone and I had to pay to get my phone back in the same condition. I told the guy that safe mode only disables 3rd party apps on the phone so this is clearly software problem, how can it cost so much? he said I must phone the repair center myself to find out. Isn't the phone still under warranty? why did no one ever get back to me with any info? I have 2 contracts with MTN but will not re new them after this incompetence.