No service while updated

Are you getting a "Cellular Update Failed" notification? or a ⚠️symbol?

for cellular update failed, you need to reinstall iOS on your phone via iTunes. this article explains how to do that: https://support.apple.com/en-us/HT208733

for the ⚠️symbol next to no service, contact apple support with https://getsupport.apple.com/

There are two Major Updates

1. iOS Update: Released by Apple Inc: Does not effect Calls and SMS services even if not updated
2. Carrier Update: Released by Cellular Service Provider, May effect Calls and SMS, if not updated

You can manually check for and install a carrier settings update with these steps: Make sure your device is connected to a Wi-Fi or cellular network. Tap Settings > General > About. If an update is available, you'll see an option to update your carrier settings.

Update your carrier settings on your iPhone or iPad - Apple Support

https://support.apple.com/en-us/HT201270