You can deactivate anyone's WhatsApp account by simply sending an email
Digression, story: Years ago I worked in a place that, if you attempted and failed 3 times to login to your account, your account would be locked and you had to see the help desk in person to prove your identity to get it back. And of course somehow this kept happening to me (perhaps a vengeful or stupid coworker?). Fortunately they changed their methods when one week a whole bunch of people had to see the help desk after their accounts were mysteriously locked.