Apple Watch SE can't make or receive calls

Hi tofu_is_soft_lol,

Thanks for posting here in Apple Support Communities. You may want to verify in Settings that the Apple Watch currently has an active cellular plan as to may help to address the issue you're facing. See: Set up Apple Watch for a family member - Apple Support

Set up cellular and Wi-Fi

If your iPhone cellular provider supports Family Setup, you can add the watch to your plan during this step.

If your carrier doesn't support Family Setup, or you'd like to use a different carrier, select Not Now.* You can choose an alternative carrier from this list of supported carriers and contact them directly to set up your cellular plan. 

Next, choose whether to share your current Wi-Fi network with the Apple Watch.

Kind regards.

Were you able to resolve this issue? We have the exact same problem. We have a standalone Cellular plan from T-Mobile, the watch can receive SMS but unable to make or receive phone calls. We have done the usual things of ensuring that the plan is active, done a factory reset, upgraded to the latest version of the OS, etc.