How do I claim my gratuity amount?

Right now, I am serving the notice period from 60days but when i joined that time my notice period was 30 days, but right now they told me i need to serve 90 days notice period and regular basis they are doing mentally harassment. But they are not giving me yearly release. And they told me i can take LWP for last 30 days but release will do after completing the 90days. In this situation can i join any other company and can i take any legal action against my old company? And how i can take my gratuity amount?