If the screw will not unscrew, then the screw may not be threaded in the handle.
Some handles are cast around the shank - which is often flattened and serrated to fix into the handle with little chance of it turning or slipping.
If the handle is not cast, then a strong glue or resin can be used to fix it, which also means it is extremely difficult to remove.
So, instead of pliers, which damages the threads, lock two nuts together (You lock the nuts together by tightening one against the other. one spanner and a pair of pliers or two spanners needed or clamp one nut in a vice) on the thread then use a spanner to turn it.
If the double nut does not work then you will be shortening the threads - a grinder or dremel is quick and easy. Even a hacksaw... Tidying up the thread after cutting is best done with a thread file, but a triangular file can also be used. Winding a nut off and on is a (poor) substitute as it leaves sharp edges and burrs which can easily cut you.