Can a rental car company charge a card you used on a previous rental?

I got into an accident. I was 100% prepared to pay the damages ($1600) in payments, like discussed with the manager. The card that the car was rented on was maxed out. They went ahead and charged a card that I had used once to extend the rental (we do monthly rentals and extend weekly). So, the only authorization they had on paper was for the original card. They only had a verbal copy and authorization on the second card. Is it legal to charge that $1600 to the second card?