Manager Threatening Clearance Over Missed Targets During Resignation: Legal?

Hello Sir, Don't disclose my name, I am working in boarding school from last 2 year's, last year principal changed and he is giving lot of work (harassing staff ) so around 50% of staff left the school. he is not appointing new staff also. hardly 2-3 staff he has appointed. In my department 3 staff ware there now I am alone, he is not appointing any one, so I am alone handling all the classes. he has increased the work also. So I decided to leave the work and I got the work also. I have sent my resignation letter through mail. In my appointment letter they have mentioned “During the probation period your service may be terminated by ONE MONTH NOTICE on “either side or Salary in lieu of notice” and The relieving date in all circumstances will not be earlier than the last day of the academic year unless the school terminates. if you are working on any assignment when you tender your resignation such assignment must be completed to the satisfaction of the school before your services will be released. As allocation of subject teaching is a duty allocated for the academic year the reliving date will not be earlier than the last date of the academic year in which the resignation is tender. The school does not encourage mid term session dis continuation of services. School academic year will ends in April. At the time of appointment they have taken all my original certificates. But when I sent my resignation with one month notice period they replied as per your request, you will be relived after the completion of required formalities and work as per service rules. But, yet they are not mentioning what are the work to complete. After one month notice period immediately I have to join my new job. otherwise i will miss my opportunity. orally simply they are extending my date. At present they have extended 15 days after my last day of my notice period. kindly guide me how to solve the problem, get back my originals and join my new job smoothly. Regards

My manager is harassing me and want me to resign from my post as she want another candidate which aligned for same role

Theres no harassment. Still i want to resign as m not able to handle