I have got the same problem, the issue that causes is that sony doesn't care much about their phone now, and therefore, they have created very bad smartphones.
I had bought xperia u and it was amazing phone, it is still working without any problems and therefore, I bought this new xperia but they have just not given that much effort.
I have brought this phone two years ago, but till now, I have only faced problems as such..
I had to go 4-5 times to sony center to rectify my problem and still I am new problems everyday.
throw it away and buy a new phone.
