Stolen phone iCloud issue

My 14 year old son had his phone grabbed today. We’ve cancelled everything we can think of but when we try and log into his iCloud account on one of our devices it keeps sending a verification code to the stolen phone which is next to useless! He has no other secondary safe device set up so we’re stuck in a permanent circle of verification codes being sent to the stolen phone. How the **** do we bypass this when we can’t find human to talk to?? Any help much appreciated!