Can I get compensation for the injustice my employer did?

Hi everyone I worked for a school for three years. When I joined, they made a contract of PRT teacher for me and asked me to join as primary teacher. But after I joined, they asked me to teach secondary classes which was not in my contract. I told them that I have been appointed as a primary teacher. Still they said, since you are on contract, we can give you any class to teach. They promised to upgrade my contract as TGT teacher next year. But again they did same thing. Then lockdown happened and I couldn't get chance to talk to them regarding this during initial months of the contract. Later I discussed it with accounts department and they told me that due to pandemic we are not upgrading the contract and if we'll upgrade you as TGT in contract, your salary will also increase, which we can't do right now. And they asked me to co-operate. I did co-operate and taught secondary classes again. When third year started, I went to talk again to the Principal. She insulted me and said write application for this and we'll review next year. Now last month in the end, without any warning or intimation, Principal called me and said we are not going to upgrade your contract and your services will be discontinued and gave me reason that your work was not satisfactory. Also, they didn't give a copy of my contract to me for all these years. When I asked for that they said we never give this to our employees, however, in contract it was mentioned that they are giving a copy to the employee too. When I insisted that I should atleast have some document for proof that I have joined your institution then they gave one photocopy of a paper where its mentioned that I am on PRT contract. I know I have mentioned a lot over here and it will take a lot of time to read it completely. I would request to kindly help and guide me on this. How can I stand up against this injustice?