Charged for pre-existing window chip

I hired a car at King Shaka Int. It had a small chip on the windscreen which was noted on the inspection sheet. I drove to EC for a funeral where it was extremely cold. Driving back to KZN, the chip expanded and became a crack. I explained and it was acknowledged by the inspector. I was charged R3k on my credit card anyway. It was the last time I booked with them.