DO NOT use great force to remove the seat post. You just might damage the frame dramatically. In my case, both seat stays broke loose from the seat tube lug. Rather, if you want to trade the frame for the correct post, I just might be able to help. Send me a PM if you are at all interested. And...

If I were to vote, it would be to save the frame set. This, to me, is a no brainer, and no offense intended with that comment. Just try to find another seat post = no problem. Find a similar frame = bonne chance! And, for all you know, the seized portion of the post might well be oxidized ugly.