Should I file an FIR to recover money lent to someone by grandmother

Dear Legal eagles, Background :My mother,75 years had lent 50k to Mr X. acknowledged on piece of white paper mentioning the tenure and amount duly signed by him and his wife on a revenue stamp.The format of the document is NOT of a typical promissory note.3 yrs have passed & payment has NOT been made.only 2k was returned during demonitization on old 500 rupee notes . Payment Mode :2 cheques were issued ,25 k each. One of the cheque has signature issues, so we paid 25 k in cash. However we have a copy of the returned cheque as well. Steps taken : . A legal notice was sent vide express post,2 months back asking to pay within 15 days but he never turned up. Just week earlier, Mr X had met my mother just outside the SBI bank & he threatened with consequences. Query : 1.If the police tries to recover the money without registering a formal complain, would that be a safe idea? 2.Should I file an FIR / GD ? And should I inform the local authorities? In anticipation