Is the seatpost aluminium? Ammonium can be used to get out a seized/stuck aluminium seatpost. Pop out the BB, pour some ammonium in the seat tube and let it soak upside down in the tub. This will only work if it is mildly seized. I had a ***** of a time get the seatpost out of my Ciocc and ammonium didn't work so I put a blowtorch to it....aluminium cools faster than steel so it will loosen up that way. Took a few trys of heating and cooling but it came out eventually. This of course means you will need to do a repaint.