Hi
Did they issue a termination letter .if not aproch a teachers organisation if any and ask them to interfere.
Is there a way to meet your management /trustee and give a complaint directly? If so try that.
Since there was no appointment letter the school will be safe as there are no terms of appointment violated.
You should also approach the district education officer with a complaint regarding the I'll treatment,since it is a private school any notification from the DEO will irk the managent. Actually management should know about the situation
Taking a legal action you should approach a court to get an order to reinstate you orelse give your termination compensation.