vende refuse to come on date for registration

on the month of may 2019 we kept for a sale one property. one party came to us finalize the rate like 80lakh.. that day they have given 15lakhs amount and asked me to sign the agreement document, I've asked them 50% of the amount then we'll sign the agreement I said.. and I asked them to take the money back,but they refused and said no issue keep it with you they said.. while that time we wrote in a WHITE PAPER the property details and the amount which they given with postal stamp ie 1RS Which taken and kept the sign and they said in one month registration will be completed.. but till today no one came to us and they refuse to pic my call.. so please give me some resolution regarding this issue..note:- in White paper we Nd they haven't included any deadlines only due amount is included..