I'm unable to activate my Apple Watch with my cellular provider.

This is a user helping users with tech questions, we are not apple and apple do not read your posts here

if it was me then I would start with your carriers support

If you wish to reach out to apple then try  Get Support (apple.com), or  Contact - Official Apple

Support

this is a user helping users with tech questions, we are not apple and apple do not read your posts here

if it was me then I would try reading

Apple Watch Cellular Not Working? How to Fix The Problem (lifewire.com)

If you wish to reach out to apple then try  Get Support (apple.com), or  Contact - Official Apple Support

Or provide them with feedback Product Feedback - Apple