RIDICULOUS SERVICE

I have a cell phone contract running for more than 4 years now. i recently ungraded my contract to a samsung s6, this was done in May. the phone worked well until last month. the phone started heating up alot and then eventually it froze and heated to a point of which, my cover started softening. i went into MTN Chatsworth as that is where i took my contract, i was advised by a guy named Andrew that its best if i send it for a quality check and if there was a major problem, it will be replaced and that this process takes 7 days. After 9 days or so i received a call from a guy that couldn't even properly explain what was happening, all i understood was that my phone was in the shop. when i fetched it, i was advised that they did a total software reload. within 3 days, my phone started randomly switching off, eventually it didn't come on. i tried taking it back to MTN today to which i was told that it will probably take 15 working days to be checked again and that i should take it to the Pavilion branch, they will help me there as there is nothing they can do for me now.... i am paying around R550 for a phone that doesn't work!! i believe that i should receive a new phone.IMMEDIATELY