What to do if someone is harassing me for money?

Actually my grandfather gave his personal savings to us that is about 30 lakhs in his full will and with due respect, we did not force him at all then he started living with us for about 2 months he was very fine playful and we all were very happy one day he went back to village for some work there my father's elder brother met him and I don't know what he told him but when my grandfather came back he started acting weird and falsely accused my parents that we miss treated them and started demanding the money he gave us, now he us calling our relatives and trying to harass us by sending letters also my father's brother is sending letters and disturbing us and demanding money, which is safely in our bank account I wanted to know is there any good way to stop these people from sending these letters and calling us and abusing us