Rent out property sell

Madam/Sir, My paternal property was rent out by my chachaji in 1999. He passed away in 2006. The tenant is a liquor dealer and has political connections. My father asked him to leave the property so many times. The property is in a village called prithvipur. And my family was in a small town " Tikamgarh " then. I have younger sisters so my father was afraid of taking any legal actions. But in 2014 October he went into an agreement of sale of said property. The very next day he passed away. The tenant filed a case that they have ownership rights of the said property being they are living in that property for a long time. Now the sale agreement was with a politically sound person who could reoccupy the property for rupees 3 lakh. But verbally he consented to give us rupees 20 lakhs. But he never gave us full amount since October 2014. He lost all the elections and thus he has no power in his hands. The property was in the name of my father. Being his son, can I cancel the contract ? Because the property is built on a plot of 10 thousand sq.ft area and it's worth is far more than 20 lakhs. Can I get back the ownership from my tenant? Please guide us.