How do I get my money back?

What is the name of your state?What is the name of your state? Missouri

I received notice that I owed an additional few hundred dollars to the IRS from 2002. I paid that.
Then I filed my taxes for 2004 electronically. They sent me a refund, minus the few hundred that I owed. BUT, I had already paid it! It's possible that it crossed in the mail as I had only paid it a few weeks prior, but I paid it electronically also so they should have had it applied.
I tried to call the IRS but can't get an answer. How do I go about getting that money back now?

Okay,
I've spent a couple of hours by this point on the phone with the IRS trying to get someone to answer my question. I can't get a real person or find a damned option that would relate to me.
I've also searched the IRS website and can't find an answer nor a way to contact them except by telephone!
Any suggestions would be welcomed