See if you can remove the SIM card and then reinsert it back into the iPhone. Does this resolve the issue?
If the above does not work, then contact your carrier and ask them whether the SIM card is not active OR whether they have turned OFF the cellular service. They should be able to provide the support that you need to activate the SIM card again.
See if you can remove the SIM card and then reinsert it back into the iPhone. Does this resolve the issue?
If the above does not work, then contact your carrier and ask them whether the SIM card is not active OR whether they have turned OFF the cellular service. They should be able to provide the support that you need to activate the SIM card again.