Registration through compromise decree

Person A is the owner of the property , he enters an unregistered agreement of sale with person B on 1991, and later in 1992 'A' executed a Registered GPA to 'B' . 'A' he acknowledged entire amountON 1992 , In 1994 the land was acquired by Society for forming layout then the owner 'A' issues notice to 'B' cancel GPA , In 1995 He registered the cancellation of GPA unilaterally . in 2005 the property was deleted from acquisition . In 2006 'A' executed a agreement of sale to 'C' . C published it in newspaper he dint receive any objections to purchase . In 2006 'C' files a suit for specific performance of agreement . IN 2007 Compromise decree was passed Now GPA holder B sells a portion of sites in that land Telling he had filed a case in 1996 for specific performance of agreement 1991 and revoke the cancellation of GPA as null and void he got a ex parte decree . Now C files a Execution of Compromise decree (2007) in 2012 and gets the sale deed through court commissioner My question is whether C has his right how can he protect his right