Procedure to obtain property in my name if there are no documents

One of my friend convinced me to buying his flat at Mumbai suburban. He had taken the flat from the first owner during the building entered in to redevelopment (Mhada), as a case the flat was not transferred in his name and the POA is registered also his agreement is registered in 2011. We bought in 2013 from our friend, our agreement could not be registered neither POA , today the building is ready builder has not yet given OC but has given keys. Keys were given to the first owner as it was not transferred on my friends name, but he got the keys from 1st and gave us. Today we are in possession of the flat, and came to know that this flat is in court case due the above reason. We have paid the full amount and all originals are with us including share certificate. Society is creating problems by saying they cannot allow us to stay as its not on our name. How can this be legally on my name, and how to stop society from harassing us. Need your guidance