Hi Alexander, expansion bolts are not intended for downward tensile loads as you have explained. If you were screwing the mounting bracket for the punchbag into a wall, then that would be a different matter altogether, as it would be a downward side load that would be acceptable.

You need to make sure that you are fixing centrally into one of the ceiling joists and not relying on attaching to the plasterboard alone as otherwise it will bring the ceiling down. 

Ideally you should be using a long threaded eye bolt secured at the top of the joist with a large washer and nut to spread the load. You could drill a clearance hole through the joist [to allow the threaded to pass through] and then using a large flat wood bit, drill clearance hole through the floorboard [say 32mm diameter] to allow a washer to be placed on top of the joint, secured by the nut then fill the hole with a wooden plug. You could try using a large wood screw threaded eyebolt [similar to a coach screw] and going at least halfway into the joist if you don’t want to have access from the floor above.

I trust this helps and don’t forget to ‘duck & weave’ when the punchbag is up.