Car Rental Nightmare: Hertz's unjust Rush and Mysterious billing Tactics

I have a car rental cover with my insurance King Price. My car went for repair at Auto magic panelbeaters. I got a rented car from hertz car rental and was to return it to Jet park branch. The date for repairs to be finished was moved twice by panelbeaters with the insurance informed. A day before date of collecting my car from panelbeaters (which was a holiday and panelbeaters closed). Hertz car rental called me to say I need to return the car. I told them that the panelbeaters is not finished with the repairs on my car and that is not the date that the panelbeater said they will be finished and I will only return their car when my car repairs is complete on the date that panelbeater said it will be finished. The following morning (on date given by panelbeater) I went to panelbeaters with my son to collect my car so I can return hertz rental car back. At the auto magic panelbeaters (also after many messages telling me my car is ready) during inspection of my car we found the the bumper was not assembled properly and we had to wait for them to fit it again. To my surprise as we were waiting hertz car rental sent a driver to come collect the rental car without calling me to inform. As I called the insurance and hertz nobody gave me the proper information on why were they collecting the rental car before my car is ready. The car rental driver even waited with us for the car to be finished so he can take the car which he did without re fuelling the car. Later they sent an invoice from sandton branch which included damages and petrol to the value of R400, for a petrol which was just one bar down. I've been asking for itemised billing of all damages that they claim and I'm not getting anything.