Have you got the hammer out yet?
Twisting can help but also stress, but a vertical whack with a hammer is good too.
First remove any seat tube bottle cage and screws in case the pin is bound on that inside.
Completely undo the clamp on the seatpin, insert a small flat bladed screwdriver in to the crevice (if possible) and try and wiggle it a bit - may do nothing but may loosen the grip a touch.
Squirt WD40 all around the 'pin/saddle junction. Tie a rag below to stop it running everywhere but squirt a reasonable amount on. Then leave it...for a good few hours, overnight or while you're at work is good as it stops you being tempted to go back to it.
Now the good bit, get a hammer
, a wooden mallet is good as you won't damage anything accidentally. Then give the base of the saddle clamp a whack with the hammer. Try and keep the motion straight so you'll be knocking the 'pin out in line with the seat tube. Give it a good whack, then repeat, then repeat, etc etc.
I did this once and it took about 4 whacks and all of a sudden out it popped without damaging anything. One word of caution, make sure any bit of you (particularly your head) is not above the saddle when you do this. When my 'pin came free the final whack made it release suddenly and the saddle and 'pin shot up and nearly whacked me in the face
.
If WD40 and a hammer doesn't shift something it ain't shifting.