iPhone carrier not available/Not Service

Did you use iTunes on your computer to update your iPhone?

If not, try again by setting it backup to factory settings, which should also install the latest updates for your carrier settings.

Restore your iPhone, iPad or iPod touch to factory settings

Also check this article again:

If you see No Service or Searching on your iPhone or iPad - Apple Support

Did you restore the phone back to factory settings, without using the backup, and still get the "No Service" message?

If your carrier confirms that there's no issue with your account or network, but you still can't connect to a cellular network, contact Apple Support.

If you see an alert next to No Service, learn what you can do.