This is 100% a software issue with and update from Sony. They will claim it's not, mine stopped working after a large update from Sony to Android 5, some months later (late april 2016) they issues another update and both wifi and Bluetooth stared working.
However in September 2016 the issued a large upgrade to android 6 and both wifi and Bluetooth stopped working again...
Make sure you don't take any updates from Sony - they will break it!