am trying to get a round shaped single shower handle off so that I can replace the
stem which is leaking

the handle part is a metal disc, it is first pulled slightly toward oneself, then
rotated to the left or right 180 degrees to control hot/cold

problem is the removal of the disc part

despite having replaced several stems in separate hot/cold shower handles, I am unable
to get to the stem on this handle.

have removed the one screw in the middle of the handle metal disc but the round handle
piece will not come off and after tugging it and attempting to rotate it left and
right, did not want to force it too much as the entire pipe assembly would move behind
the tiled wall, under the handle

I understand that as soon as I get the round handle off, I can get to the valve stem
but the problem now is not being able to get handle off the tip of the stem

there is no corrosion visible, have tried to apply heat (gently) and still failed to
get it off