Regarding Money

My brother has taken a sum of Rs 40,000 from one person. Rs15,000-20,000 in online mode which was also not send his(person) account and remaining amount in cash which was also taken in installments.[This incident took place almost in Feb-Mar 2023] But as a debt/proof by brother has given a blank signed cheque of my father. My brother has returned almost Rs 20,000 online which was also not send to that person account but friend of him. Net remaining amount was Rs 20,000. But after few days the person started to calling at home and directly asking for Rs 90,000.[August 2023]. Few days passed on phone calls arguing that the amount remaining is Rs 20,000 and how he is asking for Rs 90,000. Later the person mentioned that he has a blank signed cheque so as an advantage he deposited the cheque in bank writing the amount of Rs 90,000 on blank cheque. But between the days when arguing was going on phone call my father has blocked the cheque.[August 2023]. As the person deposited the cheque in bank, it was bounced. So he send a legal notice in which he stated that " my brother has taken Rs 90,000 from him in offline mode(cash) and in return my brother has given a fraud cheque and has cheated him and has to return the whole amount(Rs 90,000) within the 15 days of notice." Again few days passed by on phone calls arguing about the total amount. And a meeting was fixed with the person. My father thought there was no any option than retuning the amount (Rs 90,000) . So somehow he managed Rs 45,000 . The meeting was arranged.[September 2023] During the meeting the person took the phone of my father and brother then was on a call with someone (may be advocate). After arguing the person was ready to settled with Rs 60,000. So, my father gave Rs 45,000 to the person (Rs 35,000 in cash and 10,000 online). Again the online payment was sends to someone's else account which the person has mentioned. And no photograph or video recording or nothing was taken as proof for cash. The same day at night the person call arrives and again starts asking for the whole amount of Rs 90,000. Then what should one do?