If you're in the 5 boroughs of NYC, then you need not worry. Here all the laws are geared towards the support of tenants (as majority of the NYkers rent unlike other cities/towns and lawmakers gotta keep them happy). Just let the owner know that you'd inform the NYC housing dept about him not returning your deposit...I did the same to my previous land lord a few years ago as I only gave him a 15 day notice (and he had always told me to let him know a month earlier...but sometimes plans change and there is nothing we can do about it). As always, I got all the money back with threats of complaining to the NYC Housing department and a few threats of calling the police too. Now, I feel you should Let your landlord know that according to the law, he should return the deposit back with interest. Also to add fuel to fire, tell him you would've let go the interest but since he's acted like a dick, you will now take every penny of it....Then smile as you see his face frown with fear and anger.