Phone number keeps deactivating for iMessage and FaceTime

Has anyone experienced their iMessage phone number activating successfully, then deactivating by itself later?

Calls, SMS, and Wi-Fi Calling all work normally. My Apple ID email works with iMessage, but my phone number shows “Unavailable for iMessage and FaceTime.”

I’ve already restored my iPhone, updated iOS and carrier settings.

Any ideas? Was it an Apple issue or a carrier issue?