Father invested money stop receiving interest how to ask money back

My father has investd 2lacs with my cousin for invest purposes and for which he receives 2% per month interest. Till recently my cousin was giving him the promised interest of 4k per month however he has stopped giving that amt since the last 6 months. He has a agreement for this transaction on a bond paper and has also given a undated chk of 2 lacs (principle amt) and 3 chk of 4k each. However when my father asked him to return the principle amt of 2lacs along with the pending interest, my cousin has refused to do so. He even abused my father for asking him to return the amt. What shuld we do