Local guy blackmailing my mom with blank cheque

My mom and dad borrowed 1lakh with some local guy near my home . My dad know him very well for past 20 years .since we can't pay interest, I took loan from bank and We tranfer that amount in 2016 Dec to that guy. we have all transactions id and details . My mom asked blank cheque to that guy but he said I missed somewhere. My father passed away 2years before by knowing this info ,yesterday Aug 28th 2022 two rowdy guys came to my home and stating you borrowed 3 lakh rup from that local guy with interest you have to pay 6lakhs . They shown that blank cheque to my mom.she shocked. They said if you refuse to pay we'll send you legal notice . My mom said I ready to face it .. they talk very rude to my mom. We thought of complaining to this to CM cell . They just blackmailing my mom with blank cheque because my mom is single parent . Can someone will help me that how to face this problem. Shall I give complaint to CM cell or face with legal action,? Me and mom staying alone . We're not signed any promisesory note or stamp paper .mom dad just given one blank cheque at the time of borrowing 2016.