Recovery of Investment

My father has invested 2lacs with my cousin for investment purposes and for which he receives 2% per month interest. The amt invested is used for share market investment by my cousin. It has been 3-4yrs now that he has invested the amt. It 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 cheque of 2 lacs (principle amt) and 3 cheques 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 keeps promising that he will deposit the money by end of the month or week but never follow's up on his promise. When i sent him a what's app msg with the pic of the agreement signed with my father he replied stating that "Don't talk rules with me, if you want to play games even i will play them, i will not give a single paise, do whatever you want" he also called up my father and abused him over the phone. My father is not the only one that has invested the amt. There are other ppl as well to whom he is not returning the money and is also abusing them when they ask for the money.Please suggest what should we do to recover the amt.