Decree on pagdi property - landlord is asking us to evict. please help

-I am in uninterrupted possession of a flat since last 12 years. Original sale agreement made 12 years ago. It was disputed by the seller saying he did not sign on it and case is pending in metropolitian court. -Same seller has sold the flat to another person 3 years after my sale agreement (so around 10 years ago) and now after 10 years that other person has frauduelently got duplicate share certififcate issued and got membership transfered in his name by going to the deputy registrar. Soceity was dissolved and with help of administrator and some people he went behind my back and got his name transfered on the share certificate. -Original Share certificate is with me and was with me since last 10 years.My name was not transfered on share certificate and it always had previous owner's name. I was not made party to application at deputy registrar office. I am still in possession of the flat but the share certificate and society receipts have been transfered to his name. -I have been paying society maintaince since last few years, light meter also on my name. What can I do to get his name removed from share certificate and put back the name of original seller?