Really? Did you try a smaller puller? You could try to heat it up, let it cool, heat it up, let it cool and maybe the heat cycle would free it up. But you'll have to watch you don't melt your prop seal out. Another thing would be to take a dremel/cut off tool, cut MOST of the way through it (not far enough to hit the propshaft) on opposites sides, then use a punch wide enough to split it off, working from opposite sides as gently as possible so as not to bend/damage the propshaft.
Was it an old prop with the rubber hub? If so cut the rubber off the insert and then try the gear puller again.
Do you have a picture of it?