Hey Amanda! I'm not sure what you mean. There is no option within the app to "deactivate" an account.
If someone is able to sign into your account, the most they can do is change your name, email address, and reset password. Unless they then go and also sign you out of all open sessions, theoretically, they can do all this with you still being signed in on your own phone.
Unfortunately, we don't have a history of previous information to be able to verify what the original name or email address would have been. The only credential that cannot be changed is the username.