Sony India — Sudden death of mobile even on full charge need charger to start phone

Address:	Mumbai City, Maharashtra, 400606
Website:	Sony experia mobile

Hi,
I am using sony experia M5 dual sim mobile been a year using the same, am facing this problem of mobile shutting shutting down even when battery is above 80 percent and further to add to the problem it wont start even after pressing the power button to start the phone, to have the phone started need to connect to a charger without which the phone will not start. Have already given my phone to service centre thrice, they have changed the battery yet facing the same issue.
Please arrange a solution to my problem.