File a complaint in the police station saying that the signature was obtained on the stamp paper by force. Get acknowledgment from the police station on the photo copy of the complaint. By the way if a wife gives her consent on stamp paper for divorce, that cannot be legally used by the husband to obtain divorce. For obtaining divorce on the ground of mutual consent, both husband and wife have to appear before the competent court and give their statement not once but twice with an intervening period of six months. So do not worry and if you have any further doubt, contact a local advocate, who is sensitive women's issues.