Land purchased in 1998 but not registered. Who is the owner?

Dear Sir, My father purchased a land of 33 decimal in 1998 for Rs. 15,000, from a person named Nagen Das. But they did not register the land at that time & also no deed & money receipt for the above transaction. Now in 2020, Mr. Nagen's son Ujjal Das, has has denied to register the above land. They threatened that they will take legal action & not agree to register. We are living in a village in West Bengal. This is an agricultural land in our village. The people, who facilitated the deal, are now confirming the purchase and they agree that they were the middleman who processed the deal & also our village people with us for support. Some of our Village people are told us that, record the above land. We have been used this land since then, as they have sold it to us. Now we planned to build a house in this land, and suddenly they claim ownership as the land value has been considerably increased since then. Now the reference market value is almost 4 lakhs for the same land. What should we do now? If we record the land, is it valuable? Does the land belong them? Won't the witness of the people who facilitated the deal has no value? Won't the witness of village people attestation are valid deed? What action taken by our end to benefit Please help, as my father was not far away. Chintamani Das