There are going to be times when a seatpost is just hopelessly stuck, I had the typical steel bike/aluminum post situation where they ha been galvanically welding together for 35 years, and the seatpost was so thick that even a week's worth of lye treatments failed to make any real progress. As much as nobody wants to go this route, the least maddening thing to do and the safest for your frame overall is to take the advice of Lennard Zinn:
If step 4 does not work, you need to go to a machine shop and get the post reamed out of the seat tube. If you still insist on getting it out yourself, you should really sit down and think about it for a while. Will the guy at the machine shop really charge you so much money that it is now worth the risk of completely trashing your frame?
I went this route, cost me maybe $100? Worth it.