I assume you've loosen the quill stem bolt on top of the stem and rapped on it with a mallet? Do you know how the wedge inside the steering tube works?

I had one completely stuck the other day. The wedge would not come loose. I removed the bolt and the top part of the stem, inverted the bike, removed the wheel, threaded the quill stem bolt in from below, and tapped it out with a mallet. That was after soaking in penetrating oil for a half hour or so. It came right out that way.