Sometimes the drum gets rusted onto the axle. I have had this happen before and they can be a bear to get off. Soaked it with your favorite brand of penetrating oil for a couple of days and that should do the trick along with a little help from a hammer. If not, you can usually rent a puller for brake drums. That is what I ended up having to doing. They made a pretty crisp pop when then they broke loose. Good luck.
