Help with device unlock

I switched carriers and put a new SIM in my son's phone. After it recognized the new SIM it asked for him to unlock his phone with either his device passcode or Apple ID credentials. Neither of those worked and we can't get in to the phone. If I use the account recovery, it says it will send a message to the device so we can unlock it but, of course, we don't have access to that device to access the message. No other devices are logged in to his Apple ID. Help?