Startup not paying salary and not clearing my dues

Resigned in two months because of some bad experiences at work. The employer was not expecting it hence has been delaying my salary and on the pretext of asking me one information/document after another(he asked after my resignation). I have been providing him one document/info since days and every time he asks for something else, I know he has no intention of paying me as he didn't allow me to even serve the notice period ( I requested him verbally and in the mail). Now his lawyer is asking me to give the salary of my last job ( have provided him with my appointment letter and he has done third party verification as well). Is it legal for an employer to ask for documents./ information after an employee resigns in name of his company policy? Is it mandatory to provide him with my last company salary? Can he deny me a salary for not providing this?