Reject accepted resignation and decided dismiss

Sir, i am an I.T professional. i served 19 years in their permanent payroll and now i resigned my job and joined other organisation. my resignation accepted the day after resignation then. i requested them calculate all of dues like gratuity,2 year bonus,earn leave amt etc. and pay me as soon as possible. but they did not and after 3 month they issue me a letter rejecting my resignation based on charge misuse of company resources and DISMISS me from service and said that they have reserve right to forfeit the accrued benefit payable to me which completely illegal and forcefully. they have also issued a same letter to my current employer and in addition more rubbish version in that letter. in that case there is some necessary points for me i given below 1. there is no appointment letter issued to me. 2. there is no any agreement in writing between us. 3. there is no company resource provided to me such as (car,hard drive,pen drive,lap top or anything) which is registered written and acceptance signed by me. 4. they allotted a P.C to all employee but there is not allotment register for any allotment of any resource. 5. there is no personal secured password for any P.C also mine because it was there policy that anybody can work in any empty P.C. Now they charge me that i have copy software codes,code snippets, library routine, data and data structure which is fabricated, false and without evidence allegation. they said that some of my ex co-employee witnessed it. i am sure they forced them to stand false witnessed because all employee are there paid employee and it is simple that no employee will not to see his name in company black list if they not do what they said to them to do. 6. i was not entitled any project leader or project head. all project is controlled by director and we are all the member of the team . there no written in-charge allotted to me so there is no question to handing over charges because all projects in-charge is company director himself. finally it is proved that they want to forfeit the accrued benefit payable to me. so in this situation please give me legal advice. Samir Rudra West bengal