I have no network 8.3ios

Hallo ,my iPhone 6 continuously dropping network connection after update to 8.3, every 1-4 minutes... literally.. no matter where I'm located, at home or in the office. It can be 5 bars + LTE, then next moment that's one bar, no data at all... or no network completely and just 'searching...'

It drops voice calls the same way... I've tried to reinstall firmware as well. Two times already. Same results. I feel like I bought iPod for huge price ,and my friends has same network problem in Norway.