Make one more try to remove using the freewheel tool. Remove lock nut. Fit freewheel tool. Use axle nut to secure freewheel tool tightly to the notches. Use a bench vise to hold the freewheel tool and turn the rim. Or hold the rim and use a large wrench to turn the tool.

If that doesn't work, use a hammer and punch to remove the lock ring. Insert the end of the punch in the holes and tap (hard) with hammer. May want to soak with penetrating oil overnight. When the lock nut is removed, unscrew the cogs from the freewheel body. Use a chainwhip to grab them, or - definitely not as good - try a bench vise.

After you have a few of the cogs removed, clamp the freewheel body in a bench vise and turn the rim to unscrew the freewheel.

You will destroy the freewheel but who cares, a bike coop will have a box of old freewheels for $5 each. Pick one or two that your freewheel tool fits, because if they are worn and your chain skips, you'll need to remove them. Get a new chain too.