^^^^ I can't see you will get a collar to fit the top (inside) section that will slide down and provide an interference fit - when he has 10mm poking out, and thus fk all taper to work with.

Then you are left with about clamping carbon in a vice (bad unless really evenly distributed) and also hammering (worse)
If all else has failed - especially breaking the rubber pipe straps, then nothing will give you the purchase you need on that top section.
You can't belt it, yes wobbling is fine but hammering and stuff is bad bad.
Have u really washed it out? like 100x with water and then tipping up to get sand out? I am with Joe, the water needs to come from the top and lots of movement to wash that sand out.
If you drill a hole thru the top plug who cares...? Foam filler is non structural and easily plugged up later
If it really seems ALL else has failed so maybe
if you are
desperate...: clean the bit poking out really well and glue it - upright - onto a bit of very well cleaned and roughed up steel or something, with a good epoxy. You are only going to lose 2mm when u cut it off later.
stand on the steel plate and twist / lift the outer.
Or, drill a 5mm ish hole thru the inside mast section, stick a screwdriver thru it and use that to twist / pull. The hole can be filled later, and given the large amount of area that engages at the ferrule I can't see the hole will be a big drama.