Discover Car Rentals misrepresenting themselves

I googled for Car Rental with unlimited mileage and came a cross a sight that indicated Unlimited Mileage. This site was for Discover Car Rentals. When I picked up the car from SixT I noticed that the mileage was not unlimited. I was in a hurry and by the time I collected the car it was after hours, so I could not call them to correct. I called them today after I had dropped the car and the woman who answered was very abrupt and before I could raise my query, she was already referring me to the small print. This immediately made me think that this was not the first time this had happened. I did not continue the conversation as I realised, any kind of argument is not going to change the situation. Please stay away from them.