I have a carrier plan for my apple watch but still showing no connection

Yes, everything was working till last month, and I just realized the carrier plan is inactive, verified with ISP and confirmed the plan is active from their end, and there is something wrong with my watch.

I have done the following

1. Restarted the watch and phone
2. Tried to enable and disable flight mode
3. Removed the carrier plan and add it again with the help of ISP

Please help me to sort the issue.