Have you checked out and tried the suggestions in Apple's article: If you can't connect to a cellular network or cellular data???
https://support.apple.com/en-ca/HT201415
I'm assuming the SIM card is still inserted and working…???
Ah ha, may have found the problem. I rebooted my iPad and a window came up that my SIM card was locked. This has happened before and I entered my passcode to unlock it. But this time I tried something different and clicked OK. Guess what? My cellular data unlocked and is now working.
Go figure??? Thanks for all the suggestions folks.
Now if I could figure out how to use my iPad on my big screen TV. Not just for movies etc, but everything on my iPad. Is there an app or somethin.
Thanks