Naturalization Interview Experience

I hit a major block! My interview went with no problems until the very end, when the officer said that my old A-file was missing, and no decision can be made until it's found. I'm heartbroken.

Interview:

The whole thing lasted 15-20 minutes. First, the officer asked me why did I check the box requesting the name change, I said I wanted to drop my middle name. She said that's not considered a name change, and made me initial a different check box on the application. The questions she asked were all from N400, just a few of them, very easy (what's your name, where do you work, how long ago was your last trip out of US). The officer did not ask for any of the supporting documents I had with me, no tax records, nothing at all.

The Civics test was very easy, I answered all 10 questions correctly. I then signed the back of my photographs, signed another form with my personal information on it, and then... And then the officer started looking through my file and her computer, for a very, very, VERY long time. Finally she filled in another form and gave it to me - "you passed the tests", "decision can't be made", "requested file". She said I have an older A-file which is missing, which needs to be reviewed before they can make a decision.

What should I do now?

I had very bad experience with INS before, when it took FOREVER to get my green card, because of a "missing file" when I moved districts. Not again! I don't want to wait again until they "find" it, I had enough of their b*shit to last a lifetime. What can I do?

I know I can file a lawsuit 120 days after the interview (the officer, by the way, also said they have to make a decision within 120 days).

Is there ANYTHING I should be doing in the meanwhile? How often should I bug them, and what's the most effective way?