Relax - They're not police officers. But the first thing you should have done was ask for proper identification, and if they want your information kindly request that you follow them to the nearest police station, especially since they were not uniformed and driving unmarked vehicles (and minivans at that). I hope you didn't give them anything - especially not personal information. Also hope you took down all of their license plate numbers.
I'm almost 100% certain his "badge" was probably the cutout of the backside of a kraft dinner box or something that he made just so he can harass people who have nicer cars or who he rages against.