Avis courtesy car

I was involved in a car accident and my insurance company sent me to Avis for a courtesy car. when I got there at their Soweto branch, first their speed point machine wasn't working and they don't accept cash, which means I needed to drive around to find and ATM and get cash for the deposit. when I came back I completed their forms and then when done they showed me a Polo vivo that was packed outside. and then a gentlemen came with me to go do a standard check up on the car. ticked what was wrong and checked the fuel which was full tank. then I took the car and drove off. when I returned the car the very same man who checked the with me immediately says the wiper cap is gone so I look at him surprised, first of all I don't know what a wiper cap is, then he shows that its the one at the back windscreen. so I asked him how do I even know if it was there when I took the car. He replies and says this cars wont live Avis without a wiper cap. he then makes a joke that these kind of things are ****** the most on these type of cars. I am very disturbed at the fact that Avis cannot prove to me that the wiper cap was there when I took the car but can only claim it was there. and it frustrates me that why rent out cars that are highly dangerous to drive on the road. their are putting peoples lives in danger and it is not fare. now I have to pay for a wiper cap that I don't even have proof if it was there or not. Please look at my issue it is not fair