Due Diligence not completed and Final salary pending.

Hi, I worked at a startup for about 4-5 months, i worked for them without an offer letter and resigned at the end of 5 months or so due to varies reasons. I have copies of my email while i resigned and the CEO's reply talking about the due diligence and how he would pay my last month's salary month after I quit. It has been close to three months that i have quit them and i am working for another company now. He has only paid me 1/3rd of my salary till now. He doesnt reply to my messages and at times he has talked very offensively about my work. Is there anything i can do here ?