Notice period recovery

Hello Sir, My brother in law worked in a small finance company from Mar 18th 2020. The bank is 40 km away from home (one-way) and he also had 40-50km daily travel during work hours using his bike to get customers for loans/insurance. Due to this heavy travel, he developed severe back pain. Towards the end of Aug 2020 he informed his manager about his condition. His manager asked him to take rest using the 15 days earned leaves which he had. He took rest but the pain was still there and doctor advised him not to travel on bike for at least 2 months in order to recover. Hence he informed his company about this after the 15-day leave and he resigned. However his company is asking him to pay Rs. 10, 652 for not serving notice period. It is only due to health reasons that he was not able to serve and his managers informed him that his notice period would be waived off. However the HR manager of the company has said that he has to pay the amount if he wants to get relieving letter and PF. After his resignation, he has been at home without a job for the past 2 months so he is unable to pay the amount. Please advise what we can do. Regards Rafiulla Khan