Land encroachment

Dear All, My mother own a land in Kerala which came to her as ancestral property. We recently noticed that a small portion of the same (5 cents) is in possession of another person and this plot is located in front of his house. He already constructed a compound wall around his house including his plot some 10 years before. The construction of the compound wall was done soon after my mother got its ownership with consent of my maternal grandfather on a verbal contract that the person will provide equivalent area of land from his property elsewhere. This did not happen after that because grandfather did not do a proper follow up. Recently my grandfather passed away and we came to know about this mis possession. We have proper documents for the land and receipts of the tax paid till date. Kindly advise on the possibilities of retrieving the property legally.