Default [Q]4G LTE not working

Hi
I've just changed service provider and then my phone stopped using LTE. I only get 3G or h (+something)

I tried calling my service provider to see if anything is wrong but they said that everything should be working. I tried a full wipe, wipe sd, system, data. And I flashed the latest slimrom (went from android 4.4.2 to 4.4.4) but nothing changed.

Sometimes when I try to make a call theres no sound during the call.

I think I need a new modem. Any suggestions?

My current modem is: i9505XXUEML6


Best regards Kasper