Once court rule small claims case closed can debt collector take me back to court again 2 years later

In January 2011 I went to court for a small claim debt collection....after a few showinings in court it eventually was dismissed because the plaintiff didn't show for court. But the paperwork the court show for that date say the case was closed without prejudice. Now two years later, the same collection agency is attempting to take me back to court for the same debt with a new case number. Are they allowed to do this? It seems like harrassment. i went to all the court dates before and it got dismissed do I really need to go thru all the ^(^&&^ again?