Cheque bounce case pending and civil suit for declaration of title

I purchased a land for Rs.10 lakh from one Mr. x in the year 2011 and got muted or recorded in the revenue record in my name. the price of land was including cost of development to such land. Seller did not make any improvement. Sale consideration in the sale deed is 5 lakh. In the year 2015 when i started construction on the land. A person claimed that he has purchased the same land from a Bank in auction sale under SARFAIS Act, as the same seller had made equitable mortgage with the same bank. Than on my call the seller made an agreement admitting the mortgage, fraud to me, issued cheque Rs.10 lakh and promised to return the amount. But cheque bounced complaint case under NI Act filed the same is pending and now the accused is not appearing in the court. In the mean time I found that there great irregularities in selling the land by the Bank. The procedure of auction notice publication in the news paper not made by Bank. Should I file case void the sale of Bank and retain the land.