Blocking

Open the profile → More → Block User. They can no longer message you or see your last seen and photo updates. The chat stays on your device and you can delete it.

Reporting

  • Long-press the offending message → Report, pick a reason and submit;
  • Channels and groups can be reported from their profile;
  • For illegal content, keep evidence and report it through proper channels.

Prevention

  1. Settings → Privacy → Sensitive Content to enable filtering;
  2. Restrict who can message you to contacts only;
  3. Disable "find me by phone number" to reduce stranger contact.