Is there anything I can do?

[Chung Sun]

I recently moved out of my apartment. I asked them a month a head of time that I will be moving out and to find out all necessary proceedures to end my lease. They told me everything except that I needed to submit a written letter. Since I didn't submit the letter, even after several times of going into the office and asking them, they are with holding my deposit and charging me 1 months rent as a penalty. It was written in our lease agreement but they just so happened to forget to mention it. They said that if we don't payup they will send it to the collection agency. Am I screwed?