As others said, these parts are not compatible. You've got yourself into a pickle since trying to unscrew the freewheel from the freehub body (counterclockwise) will just turn freehub body.

Here's what I would do: mount the correct freewheel remover spline-side up in a bench vice.
Place the freewheel down on top of the removal tool so the splines engage the freewheel.
Reach between the freewheel and the spokes with some big slip-joint pliers and grab hold of the freehub body.
Turn the freehub body counterclockwise. It should unscrew easily. I doubt it's been tightened with a whole lot of torque.

And don't ever, ever, try that again. Get the correct cassette for the hub and ride.