Leave Encashment denied by the Limited Company

I was working in a Chennai based Automobiles Limited company at the post of Area Sales Manager. I joined the company in 2000. I was handling a branch in Jalandhar and 5 people including sales and other staff. Company has head office in Chennai , Reginal office in Delhi and branch offices in all states of India. Two year back top management changed and they start apponlinting a parrlel branch leader so that earlier one should resign himself. They have settled all the dues of the employees who so ever have resign including leave encashment . In my case a Branch manger is appointed in the same branch where I was leading the branch. In the meanwhile company sent a code of conduct paper to sign , according to this paper who so ever will make the fake travel bills and fudged bills will be terminated immediately. During working we found that new branch manager has given some fake travel bill and some other fake bills also. About this we informed to regional manager but he had not taken any action and suppressed the same. Branch manager start harassing us due to this reason. One day due to hot argument in the office I decided to resign and sent the 3 months notice as per our agreement and wrote the company has not taken the action against the culprit and managment is protecting to culprit willing fully , now I am getting the mental harrassment from him revengefully and work culture going worst day by day so I am unable to continue in this type of work culture. management accepted the resignation and relieved me next day . They settled all my dues except leave encashment of 120 days with reason that my resignation is involuntary. I wrote him again that and given all explanation that my reason of resign is mental harrassment so I left with no choice but they refused the again by mail. Now pls advise me under which law I can claim my 120 days leave encashment and how it will be done.