i phone 6 S - Unbelievably bad phone

My i phone 6 S was booked in for repairs for the whole of Sept 2015. It was only 5 months old and i had to wait four weeks before i got it back on 2 Oct 2015. On 19 October 2015 it started with the same problem it had before it was booked in!!! They don't want to give me a new phone and my service provider doesn't want me to switch to a Samsung phone. What is the use of having a R10 000-00 i phone and u cant use it because of bad bad quality !!!!??