I know this might seem dumb, and you seem like you probably know how quill stems work, but just in case this is new to you...when you loosened up the bolt at the top of the stem, did you then smack it down to dislodge the wedge? I usually hit it with a rubber mallet, or put a block of wood on it and hit that with a hammer. If the wedge won't budge, turn the bike over, soak it with penetrating oil, wait a couple days, and try it again.