You and other co-owners had property sold by some co-owners without your consent in 2001. The buyer, who runs educational institutions on the land, is now seeking your signature and offering the 2001 purchase price. You wish to either reclaim your portion of the land or receive its current market value. While cancelling the sale deed after 20 years may be difficult, you might be able to claim the present market value for your share, though the buyer could potentially claim adverse possession.