We received a bill for driving in the toll lane wi...

We received a bill for driving in the toll lane with three people in the car. There are signs everywhere that say 2+ people is no toll. The operator said you have to have a transponder to travel in the toll lane for free with 2+ people. I have a feeling the operator on the phone was just trying to rip us off, I mean this can't possibly be true. If this is true, the state of Colorado should order E-470 Authority to remove this rule.