Can't get connection to ANY carrier

Hi! I'm having some mayor problems with my OnePlus One.
For some time I have had problems getting calls and sms when using 4G but it seemed to be a problem with my carrier but 2 weeks ago I dropped my phone and the screen broke so I bought a new screen and replaced it. After that the connection to my carrier dropped randomly and now after trying to fix it in different ways I can't get any connection at all with any carrier !
What I have tried so far:

• Factory reset


• Reinstalled CM


• Put paper under the sim for tighter fit


• Turned the radio off and on and restart phone


• Change pin code


• Replace sim-card


• Tried different carriers on my phone (my simcard worked on other phones so it is the OPO that is the problem)


• Total restore by fastboot-flashing


• Installed OxigenOS 2


• Tried all modems from the modem collection on CM and Oxigen.


• Retyped the APN by hand


• Opened the phone again and checked that all cables are connected well


• Tried manualy connect to my carrier under Network Operators

For a short time of maximum 10 seconds I got a 4G connection twice in now 3 days of trying but then it stops working again. It feels like a hardware problem BUT I can see a lot of different carriers under Network Operators but when trying to connect it loads for ever and then says "Can't register to your carrier". I called my carrier and thay said nothing was wrong from their end and when I tried on other phones it worked flawlessly.

I'm really out of ideas now and I don't know where to go from here. I really hope someone of you knows that might be the problem!
Thank you so much!