Loan recovery from a office colleague written on stamp paper

Sir, My father had given a loan of Rs.2.5 lakhs to one of his office colleague and had the same written on a Rs.50 stamp paper with nottary attestation but no cheques were taken from him. Now my father has retired. The loan was given nearly 6-7 years ago. The person had returned nearly 1 lakh from the loan amount in the course of last few years but an amount of 1.5 lakhs is still due with him and now he does not take our phones either and does not want to pay. What action can be taken against him to get our money back ? regards