Looking at it from the front, you should be spinning it counterclockwise to remove it. Smacking the wrench with a hammer is usually enough. However, more stubborn ones can be overcome by manually increasing the tension on the belt.

If that doesn’t work, catch a pry bar in the pulley bolts to hold the pump still.

If all that fails, fabricate a spanner to catch 1 or 2 of the pulley bolts to hokd the pump still.

Anything beyound this will require torches, sawzaws, and replacement parts.

Good luck.