Amount deducted from Security money

I took a house on rent on 14/04 in Bangalore through Nestaway. Rental agreement has 3 parties Me as tenant landlord and Nestaway as Agent representing landlord. I vacated the property and while giving back my security deposit Nestaway deducted 6000/- as part of painting and cleaning charges. There is no mention of amount and charges on vacating the property in the agreement. I have been chasing up with them no response from them. Finally I submitted notice of dispute on Friday as per the policy they mentioned in link below I am planning to go for arbitration. Its not about just money its about the unethical practice they are running the business. Please guide me on this matter if I have a fair case to fight. What are the things I should check and make sure before going ahead. Is there any other way or forum I can approach to get it resolved. They have also charged me GST on water tanker which is exempted form GST this is another issue I am taking up with them.