Have you tried winding the RW knob in either or both directions since it jammed?
Something that MAY have happened is with the pulling upward, the RW fork inside the camera has ridden up onto the top of the cassette.
I'll suggest rotating the knob in one direction or the other while pulling up on the knob. If it doesn't work, try it pushing down. If you wind anti-clockwise, the knob will come off, there is the lever, a spring and a washer it only works one way.