Property registry cancellation issue

I had a property 1-bhk in UTTAR PRADESH. my father was trying to sell this property in 2007 but could not make a deal as buyer has not given the full payment by cancelling the payment cheque to us. then father died and buyer is black mailing us that he will sell the property as he has original registry and started to sell our house. we filed case in lower court against his criminal offence and registry cancellation, court cancelled his registry and gave order to register office for the said cancellation. now he filled appeal in high court stating payment given by him and claiming his registry to valid so that he can sell property to others. advice the rules, previous case history, procedure to fight him and how high court will favor the lower courts order.