Rip off charges

We rented a car at the Edinburgh Airport and added a wi-fi hot spot device. This device let you use your cell phone while traveling in the car. The device was stolen out of the car and we where charged $1200 US dollars. The exact same device sell new for $200. We debuted this charge and after bank review, where told that we signed a contract that can charge where ever. We would like to just purchase a new device and have delivered to Eurocar any location of there choice registered / insured instead of 6X charge. We would never rented the device if we knew how much its replacement cost was..... Shocking