Nobody ever served me any papers. How did they get a judgment against me in Georgia ? What about me not living in Georgia anymore at that time anyway?

There are many ways to legally serve. If they had your last known address they may have mailed service to it.

So your question should be how do you fight it? But before we answer that, what was the judgment for? Is it really your debt?

They don't have to actually track you down. All they have to do is serve papers to the last known address they have for you. You would have to prove that you notified them of your move, or that they served to an address that was never yours.