The quickest way is inside the app: open the chat or group, tap ⋯, then Report user (or Report member in a group). You can also email us with the username and what happened. We aim to act within 24 hours. In an emergency, contact your local emergency number first.
Email us with the subject “Privacy request” and your username. See also the privacy policy and account deletion.
Include your phone model, the app version (Settings → About) and what you did. Never email your password, we will never ask for it.