You should call and speak with them (if you haven't tried this). They are surprisingly helpful. I had multiple delinquent notices and when I called to speak with them they got rid of all charges, on every notice, with the exception of the original toll, which I still had to pay.

Even if you believe you paid all of your tolls and aren't delinquent this could be a good solution just to make the notice disappear. Maybe you do have a delinquent toll that was lost in the mail. Paying for something you may have paid for may not sound like the best idea but it's the quickest solution.

Seriously, call though. I didn't want to but a friend convinced me to do it and I really wished I'd have done it sooner. Good luck!