Wrongfully accused and charged for so-called damages that was not noted on inspection.

Upon taking delivery of our Avis rental car a pre-check was done quite late afternoon/early evening already nearly on the dark side and heavily overcasted. We noticed during the pre inspection that tyres bit worn and some other small defects on the vehicle noted. Only to discover that the vehicle was very dirty and could really do with a good clean...inside and out. Happily drove off and returned the vehicle 2 weeks later (Filled to the brim), and again an inspection is conducted only to be pointed out that there is a small chip on the lefthand side of the windscreen. Unbeknown to Avis during the pre-check apparently. Received an sms day later informing me that R3532.26 excl vat will be charged to my account for replacement of windscreen and bumper damage. I am dumbstruck as there was no bumper damage noted upon inspection when returning the vehicle. Also a small chip on a windscreen barely noticeable will cost R150 to repair-help me if I'm wrong? There is no way in hell that I will pay for something I am not responsible for as the so called chip on the windscreen would not have been noticeable due to the dark overcasted early Friday evening and as mentioned nearly dark at that time.. Please people....DONT USE AVIS!!!! Unfortunately my insurance company handed us this rental otherwise my choice would have been much greener!.... In disgust and massively annoyed!... This is Theft!