Where to file a complain about rental apartment management cheating out of my deposit?

My lease said if i don't leave my apartment by 31st dec 2009 then my lease will be automatically renewed.
Now I left right on 31st...told super I am leaving. He just asked me to leave keys in the apt, and he will check out later.
Stupid super forgot about it and never checked out the apartment.
Apartment management are claiming i didn't leave on 31st x-(
Please suggest what to do

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