what is legal actions to take for property fraud ?

In 2006 my dad was willing to sell our house in Maharashtra state. One of my Dad's friend made the deal with one person. Accordingly The person was about to give the full payment in a year. My dad trust on him and take only 50k as token and handover keys.The deal was for 8 lakh.That person gave us only 1.5 lakh in cash in 2 yrs after requesting again n again .So after two yrs we started to search another party but That person and his wife was not allowing anyone into the house .We had not 1.5 lakh that time so we could not manage to give him back .We kept requesting him to please cooperate with us so we can sell the property to another person and will return his 1.5 lakh.but his intention was wrong from start.He started to threaten us to transfer the property by his name .All documents are by my dad's name.We are paying property tax every year. We did not lodge the complain in court because we was in financial and other trouble.The property costs 25 lakhs now.