Can't connect to cellular network

So, I have an unlocked iPhone X that I use in America with AT&T (iPhone upgrade program) and I am currently traveling in India. When I arrived in India I picked up a SIM card from Airtel and everything was great for 6 days. Today, I got a push notification from iOS which was something around the lines of 'Looks like you are using a new number, want to add it as a new trusted number?' I clicked yes because I do have a new number while I am traveling. Then I got an SMS with a 6 digit code and entered it in and I even got a few emails from Apple saying that my old phone number had been removed as a trusted number and this new one has been added. A little bit after that my phone went into permanent 'searching...' mode and won't connect back to the cellular network. Even if you take the SIM card out it still says 'searching...'

So far the things I have tried: reboot, soft reset, reset network settings, removal of the SIM, and a new activated SIM card, but nothing is working.

I have even tried to apply the latest version of iOS but it fails in many ways - from the computer it fails with a 4000 error and on the iPhone it fails saying it can't connect to the internet but it is on WiFi which was good enough to download the update.

I have made a most recent backup but I am worried that it won't come up correct after a hard reset.

Any advice or info would be awesome!

Thanks,

Ryan