I have to replace the harmonic balancer?

I have a 1991 ford probe. I have to replace the harmonic balancer in it and im having a hard time getting the old one off. The manual doesn't warn me that as I try to turn the bolt in the middle of the pulley, that the whole pulley will turn with it. So I found a way to keep the pulley wheel still as I turn the bolt. However, the bolt doesn't budge. Am I doing something wrong?- - -