What options do we have if authorities prevent building on land?

In 1974, my grandparents received a house tax receipt, but they did not pay any tax for the land. Now, we have received the land and want to build a house, but the Sachivalayam authorities are stopping us, claiming that we don't have any tax payments, and thus the land is considered government property. They say we cannot build a house. Is it possible to build a house in this situation? Please advise.