I've done this job. The bolt is rusted. It will not come out.
My fix was this.
First buy new bolt kit from autopartsplace.com. Also buy rubber bushings. Unless you are buying the whole arm and in that case you don't need to buy the bushings, they should come with it.

Then get a reciprocating saw and cut through the rubber and bolt on each side end.

Yes I'm right I've done it. It takes patience to cut through the bolt, but its the fastest way to get it out.

Make sure you use anti-seize lubricant on the new bolts so you don't have this problem again.