You should test for collision between your "mob" sprite and either the wall or your "blocker".
When there is a collision, set mob acceleration and speed (bullet behavior actions) to 0, and so the mob will stop.
In this configuration, the solid behavior is useless, and you can remove it from the blockers.
From there you can choose what to do with your mob. You can, for example change its angle, and make it look like it "bounces" from the wall.