Not receiving phone calls

I have the same issue, last time I suspect something was wrong, I tryed open message (sms) and there was a wait and then it just drop back to main menu. same with calls. Then I checked the connect info on the top it was ok (TDC 4G) then I try to shut down the phone but it hang. Force it off and start again and now I got 3 SMS!. I'm not shure I can live with this issue I would rater have a phone I can trust than this.
 
It is silly, isn't it? I've got a Lumia 1520, and if it is set on 4G/LTE, it almost always bounces the incoming calls as "unavailable". I can make outgoing calls normally. After switching to 3G, it works fine. But, that is seriously wrong and unforgiving of Microsoft, not to fix such an issue.