Refused to settle full and final settlement

Dear Experts, My wife worked in a school which have more than 50 branches, she worked for 7 months 10 days, at the time of inception of her employment they didn’t given any offer/ appointment letter to her, there is no any agreement signed. Every month they credited salary in her back account but they didn’t share pay slips to her, they also deducted amount for PF and ESI contributions (there is no such practice of sharing pay slips/ appointment letter or PF/ESI details to their employees). One day my wife officially announced her resignation and she said that, she will serve notice period for 10days due to she have to moving to home town to look after the ill health of my mother. (She didn’t submit any written resignation letter as there is no practice in their school). However she served notice period for 10days and immediately she left for my home town, School management is refused to settle her F&F settlement stating that she didn’t served 30days notice period, they hold complete 40days salary and PF amount. Please advise me what should I do now and how can I proceed.