I'd take a dremel and carefully flatten damaged slots on inside of the freewheel. It may widen the slots a little bit, but better than a bent or sharp pointed edge that will force the tool off to the side. Next, is it possible to find some copper pipe or tube to fit just inside the freewheel. If you can cut a section about 35mm long, this can rest inside both the freewheel and rise up into the tool and keep the tool aligned on the slots. Re-secure the tool with QR skewer and then take a big long wrench. It should yield and break free.