How to get back security deposit

Sir I am a student and I rented a room as a paying guest (2 students per room) in a flat in Trivandrum Kerala. I transferred a refundable security deposit of 15000 to the owners bank account on June 16 2019. A receipt was provided by the owner mentioning it as advance amount. I agreed with the owner to check in on June 30 2019 and started residing in the flat as a paying guest from the same date .But due to some academic reasons, I vacated flat on July 2nd 2019. I stayed there for 2 nights. Based on the terms said( there is what's app chat and recorded phone calls as proof) by the owner prior to July 2nd( day on which I vacated flat) the advance amount is to be settled after two months from the day of vacation . But now the owner is telling that, advance amount will be paid only by June 16 2020. Since I stayed there only for two days, there is no registered rental deed with the owner. There is no written agreement with the owner How I can get back the security deposit? Please help