Landlord not returning deposit

I occupied the house on april 11,2018 . We decided to empty the house by December but we were not sure about it because we couldn't find other house where we need to shift. Even though we shared it with our owner that we may empty the house but it's not sure. But it's an emergency for us that we need to shift in a particular area. All of a sudden we found the house and we confirmed it to our owner on 19 November. He argued we must have confirmed it before a month. But we shared our issue before two months. Now he is not ready to accept the issue and said he shall not return the deposit. We said if he don't next tenants for his home we shall pay him rent for that month. But next tenants decided to shift on 1 December,whereas our month completes on 11 December. But for their comfort we told owner we shall empty by 1 December but return us our deposit for 40 days, he agreed. But now it has been a month he is neglecting to return even after many calls. Sir we did not enter into any written agreement before it was all of oral. But the proof we have is bank transactionn