Exorbitantly charged for cleaning the car

I recently rented a suzuki ciaz from avis cape town international airport. When I received my invoice I was charged R680 for a full valet of the car. When I returned the car the drivers mat had some dirt on it and the back seat a few crumbs left over from the kids when we removed the child seat. I agree it might need a vacuum. But not a full valet at R680. A large SUV can be cleaned for R200. When I disputed the amount I was told that the charges will remain.