Regarding my original certificates and PF

I worked in a CBSE affiliated school for a year. Then wanted to resign. They promised to hike the salary. Once I agreed to continue with their promises, in July month they denied of giving increment from June. They said they will not give for 3 months. I said I will not continue if this is so. Then they increased my classes. I was teaching Grades 9, 10, 11 and 12. They added 7 and 8 as well. Grades 7 and 8 have around 38 students in each. Hence I resigned immediately. I said I am ready to serve one month notice period but they forced me to do 3 months notice period. But after November who will appoint me in the middle of the year? Hence I stopped going from July 31st. Now they are not giving my original certificates. And they have not even paid our PF amount from past 15 months. I mailed CEO requesting to relieve me and give my certificates. But he made Principal to reply to me by saying they will not release them. They are not even giving me my salary slips. They say it's not mandatory to provide salary slips hence they will not give. Plz help what should I do. I am really worried as my certificates are my assets. They have taken my 5 certificates, Class 10, 12, BA , MA and B.ed.