IMEI null after drop and screen replacement

Hey everyone,

I recently dropped my Note 3, SM-N900 which I originally got from Vietnam. It was dropped, display cracked, all black. I had the screen replaced but the repair tech didn't realize it was the international version. He only had parts for the Canadian versions of this phone. He somehow managed to replace the display despite having the correct components. He fixed replaced the screen without replacing the bezel.

The screen worked great again but I realized my IMEI is now null or "Unknown".

I can't say whether it was still OK after being dropped because the screen was black and I didn't bother trying to call the phone.

I have found a lot of threads on IMEI unknown/null but read several warnings that this can be caused by either hardware or software. A software fix won't work if it is caused by a hardware problem.

Is there any way to tell what the cause is of an IMEI unknown?
Can you distinguish whether it is caused by hardware?

If it is caused by hardware, do I have any way of repairing this? Component replacement?

Could this be caused by the mismatched screen? This thread indicates a wrong screen could put too much pressure on some components, causing null IMEI....
http://forum.xda-developers.com/gala...place-t2175895

Thanks for any help here! Really want to be able to make phone calls again....

Nathan