MTN SUCKS

I upgraded my contract to a Sony Xperia Compact Z3. This is my 2nd Sony Xperia, about 2 weeks ago the top of the touch screen stopped working (3 quarter of the touch screen was working). The phone is literally 4 months old so I thought there would not be any issue as the phone is still under Warranty. I did not want a new phone I just wanted this one fixed. When I contacted the Sony Support Forum on the phone, they mentioned it might be the hardware of the phone as it did not lose all its functionality. I took it to MTN cresta on the 4 September 2015, a gentlemen assisted me with getting the information filled out on the form. There was a small chip on the bottom of the phone which is hardly noticeable. This week Tuesday, MTN repair centre sent me a shocking quote of R1633.20 to fix the phone or if I reject the quote I need to pay back R330. When enquiring with the call centre why I am being charged when the phone is still under warranty, they mentioned due to the small chip on the phone the warranty is no longer valid, the chip has nothing to do with the hardware of the phone as the chip is in the bottom, the issue is with the top of the phone, 16 years a loyal customer now UPSET.