A small, very sharp chisel. With a small hammer try to create a cut or notch coming in at 90 degrees. Then turne the punch about 45 degrees to side , tip pointing the direction of screw coming out. Then hold tight against the notch, start tapping and seevif it starts to move. Wont need to move far to get loose.
Small vise grips, work good, jaws must be good. And screws should be changed.