Check the manual for your router. What you want is called MAC address filtering. Blacklist his MAC address. (or whitelist all of them but his, depending on what options your router offers.
That will prevent his device from connecting at all.
(Note that this will not prevent him from connecting to a different network. Maybe someone should just take the phone away from him. That's what my old man would have done, right after he tanned my backside with a belt... if cell phones had actually existed back then, that is.)