What is i blocked someone on facebook but they still message me?

If you've blocked someone on Facebook, they should generally not be able to contact you, which includes sending messages to you on Facebook Messenger. However, there might be a few scenarios in which this could occur:

1. Previous Conversations: If you’ve been part of a group conversation with the person you blocked, they might still be able to see your messages in that group. You would need to leave the group conversation to completely cut off contact.

2. Third-party Apps: If both you and the blocked person use the same third-party app that integrates with Facebook (such as a game or other application that connects users), they might still be able to message you through that service.

3. Technical Glitches: Sometimes, technical issues or glitches can occur that might temporarily allow someone you’ve blocked to send a message. In such cases, try unblocking and then re-blocking the person, or contact Facebook support for assistance.

If you believe someone has found a way to bypass the block feature, or if you're experiencing any issues with it, you may want to report the problem to Facebook's support team for further assistance.

To further ensure that the person cannot contact you, you may also want to adjust your privacy settings and restrict who can send you messages or friend requests.