Why does my I watch show no SIM on the pan and no connection on status?
Why can’t I get phone calls on my watch?
Apple Watch Series 7, watchOS 8
The article you came to the community from Set up cellular on Apple Watch - Apple Support is the best resource for this situation. If you've completed that troubleshooting and the issue is still not resolved, contact your network provider to see if they have provisioned the plan for your Watch.
or
use the link in the article to Contact Support but they will suggest thst you contact the provider first.
Click here > Contact - Official Apple Support
or phone numbers
Click here > Contact Apple for support and service - Apple Support