Getting back the original educational certificates

Respected Sir/Madam, I am working as a Computer Teacher in an permanently un-aided school for last 7 years. I am eligible to get my benifits in my profile but this school has been playing politics and has been denying to give me the same. At first when it was time for them to give my benifits they put me on observation period with my colleague saying we me and my colleague had coordination issue. They wasted complete one academic year for this.Now my colleague has left and a new person has joined who is already ill mannered and over a little debate on work the school principal says that he has resigned because of me. Though they are not presenting his resignation letter. Again in this academic year on 8th August, 2023 the school management has put me on observation also they mentioned they will issue a warning letter and will not give any increment in the salary too and if they find the result to be unsatisfactory they will terminate me or i shall chose to decide. Which they have really done so even after telling them facts but The warning letter was delayed from their end and till that time i resigned from the post stating the reason as no growth in work profile on 12 August, 2023. Now on 2 September, 2023 they called me and were giving the warning letter where they had their complaints written alongwith a sentence that is... I have been the reason for their teachers to leave their job. Which is completely a false blame. So I rejected to sign the letter against which the Principal of the school has told me that if i won't sign then I won't get my educational certificates back neither will my resignation will be accepted and the warning letter that they have drafted has a date of 8 August, 2023 which i feel makes no sense to sign as iis backdated and also i have resigned.. Also i feel taking that letter will be a false evidence against me and can spoil my future prospect.. They haven't even given me the acknowledgement of my resignation letter.. Post that there has been no communication from the schools side. I am still going to school because i feel i have resigned and i am serving my notice period to do so. I am so confussed and stressed due to this that i am not able to concentrate and do my things. As I have no proper person to guide me for the same. I have approached you and would sincerely request you to please guide for the same