Unsatisfactory customer service response to a problem with the vehicle that left us exposed

We were given a considerably bigger people carrier, in fact it was a mini-van. It was parked outside the compound in a dark street and we picked up at night. In daylight, we discovered that the sliding back window’s locking and closing mechanism was broken. We immediately contacted Autovia and their response was extremely unsympathetic: by phone they told us no alternative car could be supplied; by email they told us that we had already signed that the car was in good order. So we were left with a vehicle, one of whose windows did not properly close or lock, something which had been hidden to us in the dark of the night. In other words, we were left with a vehicle that could easily have been broken into and risked any baggage we left in the vehicle, which had an impact on our holiday.