Maybe it's the bad signal. Restart the phone and try again; Check whether there is a network, it is recommended that you can use in a place with strong signal. Check that the USIM card is plugged in. If it is plugged in and still cannot be used, it is recommended that you go to the business hall to check whether the USIM card is faulty or replace the card for a test.
First check whether the local call signal is normal, and then check whether the phone is set to airplane mode.
That's still unpaid. You need to check how much you owe before you charge it.