i had the same problem mate.
i couldn't get mine off with a 6ft extention bar!!!
I drowned the thing in wd40 about 4 or 5 times once an hour until i finally tried it and it came off! Either that or find the closest HGV specialist. They use an extremely heavy duty impact ratchet for HGVs that will take it off. So if wd40 doesn't work, have them do it, i doubt they would charge you anything for taking it off and then tightening it up again by hand.