Try one of those freeze cans? They sell them at autozone/pepboys. Or you can get a few cans of 'canned air' and try freezing it with that. Sometimes getting something very cold will shrink it and break the corrosion keeping it locked up. Warm it with a hair dryer, freeze it, warm it again, and try it.
Otherwise heating with a torch or heat gun would do it, but you cannot do that since its a strut and that damages them. Keep at it, you may need to get something stronger than a little stamped steel spanner.