M2 Aqua Damaged and doing the same thing again!!!!

I bought my Sony Xperia M2 Aqua in April this year, after two months of having this phone it went off and never went back on again, I sent it in for repairs and got it back two weeks ago, and today it did the same again, now I have to go through the whole process again, and Sony doesn't give back new phones only re-furbished phones as per the customer care line. This phone is still under warranty, and is only 4 months old. This is totally unacceptable, I want a phone that works. Please get back to me, I want this issue resolved or I will take further steps.