The only way I have successfully removed really stuck seat posts is by pulling them out with a threaded rod - cut off flush with top of frame, insert rod all the way thru, attach nuts and washers thru BB hole, gas pipe to provide space to pull up into and push against the frame, LOTS of lubrication (threaded rod and nuts get sizzling HOT). Use Heat Treated Cro-Mo threaded rod and nuts only; garden variety hardware is not up to the task.

Time about an hour after the BB is removed. Figure $50- for 1/2" cro-mo threaded rod, another $10- for hardened nuts. I can exert over 10,000lbs of force with a 12" long wrench and 1/2" threaded rod.

The frame shown is scrap steel because of a really fouled up attempt at seat post removal.