Hidden costs & dishonesty

I have been using First Car rental for 5 years as a happy renter, but this recent experience will make me not return.

When I received my final bill, I was charged for all the tolls we went through when I paid cash at all of the tollgates. When I queried this and told them I paid cash at the tolls, the response was that the car was fitted with an ETag, and that I need to provide proof that I paid cash at the tolls. Why would I keep toll receipts when I did not know I would need to dispute this?

Surely the responsibility is on First Car Rental to EXPLAIN that the car is fitted with an etag. THIS WAS NOT MENTIONED AT ALL when we collected the car. The company is basically charging and admin fee on top of the toll fee because the car was fitted with a secret etag. Ridiculous.