I rented a Van for the weekend, when I return it i...

I rented a Van for the weekend, when I return it it was on an bank holiday so no one was around. I checked over the Van along with my 6 other passengers and everything was OK. Two days later i received an email with a $1000 receipt for a new windshield and a smiley face at the bottom of the email. I taught this was a joke so I went straight back to office and asked them that what was up. They said that there was a crack and that was the minimum price I had to pay was $1000, I explained that I was not willing to pay and could I see the Van? The Van is gone..... rented out to someone else.... is this legal. I said I will pay, but that I would contact them back when I look into it. As soon as I left they took out $1000 out from my credit card.
I am sure that there might of been a very small hole either from me or someone before me and that when they were cleaning the car, the crack appeared. The best insurance they provide does not included the windscreen or any exterior part of their cars. The Van had no VIN number and the licence plate on picture did not match the receipt for the windscreen, and how does a windscreen cost $1000, do they have a partner in this. Good price and nice cars and seem nice people but they need to fix their insurance out. This cost me every penny I owned.