How can I get back my security deposit from my landlord?

Im in need of legal advice. I rented an apartment on 08-01-10. A couple months before my lease was up we contacted the landlord several times about renewal. He agreed to a $25 increase and another year. The weekend of 08-01-11 arrived and we never received a new contract. I made a last minute decision to move out and contacted the landlord to in form him we never received a renewal contract and we have decided to leave. He now is now holding my deposit un til he rents it out again and claims he will prorate me the difference because i had to tell him 2 months in advance if i was leaving. Then he also claim s once the lease is up we go into a month to month contact with him but i was out on 08-01-11! My feelings are they neglected to send a new contract, i did not break the lease it expired and its their responsibility to give me back my security. Can anyone help?