Ok, basic advise
Remove SIM card. Give it a wipe. Reinstall.
Turn off phone.
Wait ten minutes.
press and hold the Power button and the Volume down button down simultaneously for more than 7 seconds to restart it
this is a hard boot, and forces the phone to reconnect to network.
If I helped or solved your problem, please like or tick solved.
Have been using phones since 1993, and am self taught.
I offer advice for free, cos I think it'll help, if it doesn't, explain why, I might learn something new too.
Current phone Galaxy S22 Ultra
Previous phones: most S series, Note 2, Samsung Alpha, iPhone 3gs, far too many Nokia's!