Harassment by employer

My brother works at a telecom company in Bangalore and has resigned on Apr 1. However, the company is refusing to pay him for 15 days of work saying he worked from home. In reality, he was only supposed to wfo for 6 days of those 15 days. He has been incorrectly marked absent. He has suggested that they can cut 6 days of his salary if they wish to, but not for the remaining 9 days. Additionally, an ex-employee said that the company will delay his FnF amount and relieving letter for 2 months. He relies on this monthly income for expenses, and a delay can cause financial stress. Plus, his future employer may have issues in hiring if he is not able to produce a letter. Need help in deciding what he can do to ensure he gets his pay and letter on time.