Sc St land purchase

My father purchased plots in Bangalore Anekal Taluk. We had got documents from 1968 and had verified. There was no document to show that it was an sc land. Now a person claiming to be an sc and a legal heir of a grantee has obtained orders from Assistant commissioner setting aside the sale to my vendor. My vendor had purchased it from Venkatesan who had purchased from Govind who had Purchased from Muniappa(whose legal heirs are claiming). The documents did not show that Muniappa was a sc. What is the relief for my father. It is good to protect the rights of the sc/St. But, what is the relief for the Purchaser's like us. People say that ignorance of law is no excuse. But the documents or the ec did not show that it is a sc land. It was a hard earned money by my father. What to do. Moreover we were not informed by our vendor that a case has been filed for us to contest. The sale was in 2007 and the case was filed in 2009. We were not informed. The judgment is given by assistant commissioner. What is to be done to plea my findings that it is not a grant land but the order was passed. What relief can I get from my vendor. Regards, Poornima