A seat pole can seize in the frame when it is fitted without an application of grease and not moved for an extended period (a decade). It is particularly common with alloy seat poles in steel frames and is caused by corrosion of the metals essentially welding the two pieces together.
We’ve had success with this method, using a Stilson wrench (pipe wrench) with extra leverage to grab and turn the seat tube while the frame lies flat across a tabletop. It’s best with two people, one to hold down the frame and the other to turn the wrench. The Stilson wrench is an ingenious tool which will continue to clamp tighter as the force on it increases, so it will not slip on the seat pole. It will however leave teeth marks on the seat pole.
Cycle Saloon 