SONY EXPERIA M5

I got my Sony Experia M5 on 7 December 2015.I have had problems with it since day 1.I exchanged it on 8 December 2015 as it experienced sudden death and camera error.My new phone has exactly the same problem.The sudden death happens when there is low reception,but keeps on working on LTE.Whenever I want to take photos it gives an error.We have done all the software repairs and hard reset as suggested by Sony, but to no avail.We contacted MTN who told us that we need to send it to Sony as it is a warrantee issue. I asked for a replacement,as it is a brand new phone and I don't just want it repaired.Sony has told us to take it to a repair centre to assess whether I need a replacement.Sony now claims that it is a battery problem,which it is clearly not.I phoned MTN again and they said we shouldn't have taken it to Sony,but it was supposed to be booked through MTN and therefore now it can not be exchanged for a new phone.This is absolutely unacceptable as this is a brand new phone on a contract and I have had little to no use from it.I am currently working with an old Samsung S2 while paying instalments on a brand new phone.I read a few forums and it is obviously a faulty model.