Owner of house refuse to refund the security deposit and asking for extra 1 month rent

Hi. I was living as a tenant in Mulund east, Mumbai. As per my rental agreement there was no such lock in period and have to give 1 month notice period before leaving the house. My rental agreement was of 11 months starting from 16th July 2019. I emailed to the owner on 24th March 2020 and give one month notice period. In my notice I informed that I will leave on 30th April 2020. But after discussion with him, owner told me to pay rent till 16th May 2020 (rent cycle i.e. start from 16th every month which is Rs. 19,500). Even, I agreed (I have proof of whats app conversation too.) I also paid the dues (electricity and gas bills) till now. I left the house on 5th May and also the landlord inspected the flat's condition which he told perfect. Now, its been 10 days and when I am asking for the security deposit amount (Rs. 80, 500), he continuously ignoring my calls and messages and now finally when I have talk with him, he bluntly refuse to refund the deposit. Not only this he told me that he will cut my next month's rent (17th May to 16th June 2020.) Moreover he is saying that he will pay the deposit amount only when he will get the new tenant. I have all the voice recordings. My question is, what should I do? Kindly, suggest me legal advice. Thank you in advance.