I did a search and read what to do when you get a stuck seat post out of the frame. HOW DO I GET THE POST OUT OF THE FRAME 
? My husband has been trying and damaged the seat trying to pound it out. We can’t get it to budge. I suggested heating but he said that would damage the paint. I almost don’t care even though the unicycle is new. I can’t do anything with it until I can cut the seat post to fit me.
How to get it out will depend somewhat on why it is stuck. If it is a new uni it is most likely stuck because the seat tube gets narrower or has an irregular surface inside. If this was on an older uni it might be stuck due to galvanic action between an aluminum seat post, and a steel frame. This is prevented by lightly greasing the seat post, but a lot of people don’t grease seat post’s on uni’s.
I would use a penetrating oil and let it sit overnight to let it really get in there. In the past on bicycles we would fill the seat tube from the bottom (on occasion we had to cork the seat post) and let it sit overnight.
Hitting the seat post from the bottom while bracing the frame against softwood blocks (pine 4x4’s) would be a good next step (use a piece of pipe smaller than the seat tube to hit the seat post, but if that doesn’t work a pipe wrench on the post will hopefully get it to move.
In severe cases, especially when there was galvanic action, we had some luck using automotive anti-freeze instead of penetrating oil. Ultimately, if nothing else works a torch can do wonders; although, it will destroy your paint and maybe the integrity of your frame.
I’m sure there are more ideas, but from least to most destructive this is my list based on experience with bikes.
That was a pretty funny read. I happen to have one of those bmx seats sitting around.
My husband wanted to pound out the expansion pin and pound the post from below. I told him I would use the WD40 and let it sit overnight before trying something so drastic. He said it wouldn’t work and even got sort of mad. This morning it took me about 5 minutes to work the seat post out. I can’t help but feel a little smug :D.
Now I have to cut the seat post and then try to ride the thing 
. I’m sure I’ll be humbled real quick.