What are you using (with your hammer) to drive it out?
Maybe you mushroomed out the end. As DI said, find a pin
punch with a diameter slightly smaller than the hole (don't
want to get the punch stuck). You want the punch to make
contact with the entire circumference of the pin. Set the
assembly over something substantial, like a bench vice's
open jaws, so your hammering on the punch transfers the
energy totally to the pin. I don't remember the pin being
tapered, so it should come out either side. Keep at it and
something will finally give.
Jerry