Did you get the wedge loose? Just taking the expander bolt out with out first knocking the wedge loose won't free up the stem
Old Schwinn cruisers are notorious for stems rusting in the fork steerer due to no hole in the bottom of the fork crown. Water collects in there and never drains or dries out. As said above, lots of penetrating oil and patience. Handlebars on, front wheel on to use them as leverage to twist it loose. Once it turns, then you can pull while twisting.