Notary agreement for land sale

I need help for the below query. Recently one person was in need for money for which he wanted to sale a land.Looking the land my father shown interest in the deal and they did a notary agreement between them. So the total cost was 2lakhs for which he took 1 lakh at the time of agreement. Also in the agreement he mentioned that in next 2 months he will transfer the title to his name which is now on his grandfather's name. His father is no more now. Now his mind is changed and saying he will not sell the land but will return money. Also when I asked for money, he is not picking calls neither meeting. So my query is now i am planning to take legal action. So wanted to know whether the notary agreement of such agreement is valid. What action I can take.