Get a nail, cut it so that it just fits across the diameter and wedges firmly into the notches. Grab the nail with pliers and twist it, maybe use molegrips or even wedge a tiler's hammer in there for mega leverage. the nail forms the opposite of the slot in a slotted screw.
Sorry, I can't do you a pic, but this is worth a go.
wait! another method I've used. Remove the axle.
Get a nail, cut it so that it just fits across the diameter and wedges firmly into the notches. Grab the nail with pliers and twist it, maybe use molegrips or even wedge a tiler's hammer in there for mega leverage. the nail forms the opposite of the slot in a slotted screw.
Sorry, I can't do you a pic, but this is worth a go.