What if buyer didn’t pay full amount after property sale?

I have a plot in Haryana with power of attorney. I sold it to a man named Sanjay. He sold the property to two other people (dividing the land equally) but has paid me only 10% of the agreed amount. One of the new owners has already started construction. Although the construction is currently stopped, my family and I are worried that they might continue building in our absence, and we’ll be helpless. What legal steps can I take to stop this and recover my dues?