Block someone: their profile → ⋯ → Block, or in the chat → More → Block.
After blocking:
- They can't message you, call you (not even your regular line through Tellu) or send you a friend request.
- The friendship between you is removed.
- They don't see your status, last seen or moments, and can't find you in search.
- They can't send credit to you, and you can't send it to them.
- In shared groups: their messages don't reach you.
- They are not told that you blocked them.
Unblock: People → Add & manage → Blocked users → Unblock. (The friendship doesn't come back automatically — send a new request.)