Property document stolen by co partitioner and sell of property

My grandfather owned a room in one of the main area of park street Kolkata under the pagadi system(tenancy model). After his demise the room belong to his 2 sons, My father and my uncle. My uncle and his family were residing there and they didn't want us to interfere in such property. But somehow me and my mother were able to tackle the issue and made a partition of the property with a plywood. My uncle and ant had stolen the property document from my grandmothers box when she was alive. And Now