I phone 5s microphone & speaker not working

hi i buy a I phone 5 S in march from E max UAE . Its been 3 month only but my phone audio jackpot is not working ,microphone and speaker is not working moreover if i open some app for longer time and during charging it get hot. I took the phone to the store tell them the problem and the phone is in warranty also but they didn't change the device they say we cant change and just repair the device. its been two days my phone is back again i am facing the same problem .can anybody suggest me where should i go for complain and what i will do to change the device.