Hello KayMorris,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with using cellular service on your watch. Try the steps here to see if they resolve the issue: Set up cellular on Apple Watch - Apple Support
If that doesn't help, try the following:
- Ensure the same Apple ID is signed into Watch.app > General > Apple ID, Settings > [Your Name] as the iCloud Account, and Settings > FaceTime. Let’s also ensure this is the Apple ID signed into iMessage
- Ensure that all email addresses and phone numbers are checked on Settings > FaceTime and Settings > Messages > Send & Receive under ‘You can be reached by FaceTime/iMessage at"
- Verify Wi-Fi Calling is enabled (HT203032)
- Turn on Calls on Other Devices in Settings > Phone > Calls on Other Devices
- Enable Wi-Fi Calls on iCloud Enabled Devices via Settings > Phone > Calls on Other Devices (simply tap the banner, it will go away when activated)
- Ensure you haven't by chance blocked your own number or Apple ID in Settings > Phone > Call Blocking & Identification (Also, remove any third-party apps you may be using here).
We hope this helps.
Cheers!