Fake Stamp paper

We purchased land in 1990 thru oral agreement from one of our relative, after getting possession we constructed house on that land, installed first electric meter in Jan 1990 and also other gas meters as well in year 1911-12. After death of our relative again we entered in new written agreement on 3-9-2013 with his son, we requested him many times to give us Khata but he gave only false hopes as always he replied we are one family who will threat you if am here, Son also died in Jan-2014. After the death of that son his foti Khata was changed to his legal heirs & again they Sold our Land & House to other party in Dec-2015. We put civil suit in district court and all our Oral & written Agreement witnesses with notary public are appeared in honorable court and recorded their statements accordingly in our favor. Now the matter is that the stamp papers provided by seller in year 2013 are fake and as per stamp superintendents record this original series of stamp papers are issued in Jan-2015. Now the question is that if all witness (Oral & written) are appeared in court but stamp is not true then what would be the status of our case in future or what would be the status if our one side of Oral witnesses is true. Please it is my humble request to guide me, what law would support me if all statements are true but stamp paper is fake Or if only Oral witnesses, bills, house possession etc are true then how would my case would strong. Thanks a lot