I just taught a stubborn user to stop using his personal wifi on the company laptop.
I could see this user kept routing the internet from his personal phone to use it on the company laptop (maybe to try to stop us from spying on him)
Instead of being a normal person and a competent SysAdmin, and properly adding a GPO to restrict the available Wi-Fi networks, I used the MDM to remotely download a 20GB ISO to his temp folder.
When the download was at 18GB the download speed went down to less than 50kbps. So I guess his data plan is over. By the next hour, I could see the laptop was connected back to the company wifi.
He will never do it again.