Private money lending and threatning.

Hi, I want advice regading private money lending. I had borrowed 6lac rupees from a friend in 2015, sep. He said u have to repay with 20% monthly interest. I accepted since I was likely to get a bank loan cleared in sometime. No contract was made. He gave me cash and took a blank cheque. Subsequently my bank loan disnt go through I suffered a car accident and my business (reataurant) closed down. I paid 2 lac ruppes as interest for 8 months and then futher paid small amounts, so far have paid 21 lacs and still the person is asking for 20lacs. He is threating me and my family. I dont know what to do, please advise urgently.