Phone number not available for sharing

I’m at my wits end with my iPhone … I try to activate my number, it says my number is unavailable for sharing I can’t even select it or delete it. When I tried activating it on the message section it said that it was unsuccessful. I’ve updated my phone to latest iOS my phone and tried turning my things on and off including my phone itself then back on but still cannot choose it in message. Can someone please advise … many thanks