Bought a property with POA from A who died his son not giving property

I bought a part of the land from a person 'A' and got power of attorney because at that time (3 yrs back) registry was not available. After 3 years the person 'A' died and his son got the registry of the entire land of his father in his name, which includes my land also. Now the son of person 'A' is avoiding talking to me to resolve the issue. In this case what should I do? Do I have rights on the land bought from person A (power of attorney). Even when his son got the registry in his name? Thanking you.