All calls go to voicemail. User Busy.

All incoming calls go straight to voicemail. Phone shows a quick splash screen saying User Busy, then missed call notification.

Watch checked at Apple Store. All tests, good. Refered to carrier for a replacement SIM card.

Sim replaced. Trouble persisted.

Found apple watch connected to phone by cellular network and bluetooth.

Turned bluetooth off on watch. This fixed the problem.

iPhone 12 Pro Max. Apple watch series 3.