Forced to resign

Sir, I worked in a so called Montessori school in Hyderabadfor more than 3.5 yrs. I was never given an appointment letter inspite of asking several times. Salary was going into my account for all these years. In mid Dec 2019 I was asked to resign by HR with immediate effect by whatapp message. The only answer I got was that I spoke to the parent rudely during PTM and their child gets nightmares because of me. I was not told which patent or which child. I was called the next day, that too after school timings to collect my relieving letter. Before that they asked me to send resignation as termination does not sound good. I asked them to pay one month notice but they paid me only for 15 days. I am not able to get a job as I am being questioned why I left the teaching job in the middle , that too if term is coming to an end. For me money is not important but I want to tell everyone that the founder is a big cheat. They never gave me appointment letter. I have all the mail's I sent to them and the WhatsApp chats