It took time to put it in there, it will take time to get it out.
Make sure that an old saddle is securely fastened to the seat pin.
Spray some WD40 or similar on the pin.
Leave.
Repeat as aften as you like but give it time to soak into the micro gaps between frame & pin.
Come back in a couple of days.
Remove pinch bolt completely.
Drive suitable wedge in paralell to seat tube to open seat lug slightly between the pinch bolt lugs.
Use small cold chisel or largish screwdriver but be gentle & just ease the pressure from the seatpin.
Grasp seat firmly, apply rotational force. If seat pin moves just a little, then apply a little light oil &
wiggle gently. The objective is to get the oil in, not so much as to get the pin out, .... yet.
This might take a couple of days but if the oil gets right down there it will be so much easier when you do give it your all.
When you think it's time, try to rotate the saddle round & round then wind it out.
Good luck