Contact the church they should have records of the purchase. There are probably no deeds or receipts. When my parents bought a plot years ago they got a 'Cloakroom (raffle) ticket', we were told several times over the years of location and importance of said ticket.
It was always wondered about the legitimacy of this ticket/plot, as it turned out the priest had sold them to raise money for his own purposes. More recently a relative died and to cut a long story short my parents offered the family the plot. Enquiries were made by the undertakers and it turned out the church did actually have a record and the special Cloakroom ticket was never needed.