Disabling * 69 Feature

Where do I disable the call back feature.

I want to block a group of users being able to dial *69 to make a call back to the last number that calls them.

well I guess in your dialplan it is allowing the person to dial *69, so I would look at extensions.conf and modify it so a user cannot dial *69, and you could even send them to a message saying that feature is not enabled or something.