Leave Company without Notice Period with NO Appointment Letter.

Hello, I have Joined one proprietorship company on August-19 till May-20. Company has invited to join, earlier I was earning Rs. 70K PM salary, but this company request to join with Rs. 53K PM Aug19 to Dec19, after from Jan20 they will increase my salary. I have joined by his verbal without offer/appointment letter/Salary slip etc. because past i have very good relation with his owner. I have waited to increase my salary till Feb20 but, they have not given, I decided to left him and gave one month notice (verbal) period on Feb20 end. during the salary time they have put hold my salary because of insecurity feel. After that, on March20 they have verbally communicated with increase Rs. 70K, I have said OK to work but, because of COVID19 situation on April20 they have said they can give Rs.53K to me I verbally ok because of the situations, that time they have paid my salary (march20) Rs. 40K and 13K put on hold, i have requested him several time to release but no revert, on May20 they have mailed me one doc to sing on computer stationery paper with computer print to sing for minimum commitment december20 if i leave on or before dec20 company can claim three month salary, otherwise they will not release my May20 + April20 balance salary. because of COVID19 situation by forcefully i have to sign it coz i was not having any options. i have decided to not work his company as they have never gave offer/appmt letter/salary slip etc. from company side. on June20 i have verbally intimated to company owner to not continue and i am ready to leave my May20 month salary, they are forcefully trying to retain me, using abusive language over the phone, i have submitted all company assets as there was no any written evidence from company side. now, company is claiming Rs. 60K to me otherwise they will spoil my image reputation to the market etc.and some places they have put the mail also, several people has intimated me about the mail and still they are following for money. As I am having no offer/appointment letter/salary slip etc. even company is not paying professional tax to govt. please advice what to do.