Cancellation of agreement of sale for not having original documents but buyer refused for the cancel

The documents we have are sale deed , digital kata ,23years tax paper and EC on my name but our property is not registered but notarized and we do not have original documents as its with my mom she refused to give it so I decided to sell it with Xerox copies but I have sale deed and digital kata as certified copies with only these documents I made an agreement of sale for plot was 75 days.so the agreement of sale indenture was made on 3rd day of October 2023 for 75 days as soon after the agreement he removed our plot saled board and replaced it with his name board . The problem is the buyer said he will get his registeration within 15days days on the agreement day, but after 30days, he asked for original documents were we don't have, what we have are sale deed and digital kata as certified copies and the buyer asked for his registeration to be done by us and asked for the linked documents of plot.so I decided to cancel the agreement and pay back his advance amount but after some days the buyer send me a police notice on 21/2/2024 for the registration and for link documents of plot and called me to the police station were I decided to cancel the agreement but the buyer is not ready for the cancellation bcoz the buyer asked double amount of advance amount for cancellation or get his registeration done by us.so what do I do for it . should I send a legal notice for cancellation of agreement and give him his advance amount but not double amount of advance amount.