Getting threat from my former employer

I joined a startup when I was in college 2 years back as co-founder( which I was told). There were no employment documents signed only NDA and non compete. I was working as CTO and developed sme significant tech. I worked their for around 2.5 years with no salary and equity. After college i decided to go for phd and i quit. Now I asked for some money for my time and now he is refusing to pay me and threatening me with NDA and non compete. He also mailed some screenshot(i abused him once) to my College HOD to cancel my phd and defame me. What should I do legally? Are nda and non compete valid?
Location: Bangalore