Landlord refusing to give the security amount

I have taken a property on rent in gurgaon, there was bo agreement made by the landlord saying it’s a owner property and no broker was involved, I was not told about the lock in period even in their website it says “no lockin period”, after 3 months I decided to leave the flat and asked the owner’s manager about the procedure, he simply said “mail your notice to the owner within 10days” I did the same, and after that he was sending different tenants to the flat for a visit, even I told his caretaker (who manages his all the flats) that I am leaving the flat, I have seen flat somewhere else and he accepted that, now on 27th (month end) the owner is saying you can’t leave the flat as you haven’t completed the lockin period, and he will not refund the security, I asked him why he’s telling this on 27th, when I mailed him on 10th he could have informed me within 1 week after the mail was sent, the excuse he gave was “he was busy somewhere” after so many arguments, he said he will return my 50% security or if he find new tenant within 10 days he will return my full security, but the question is where is my fault here?