Overcharged no explanation hidden cost

My son rented a car thrue Drive SA with a standing quote that had to be paid ,he paid the deposit of N$218. Adter returning the car in Oranjemund on the 1th of December 2017 he was charged an extra day a one way fee and underaged fees. The one way fee was never explained or in the quote we accepted the underaged fee. For an international person who is not explained what is hidden in the cost and have to pay nearly 15000 for a 3 day trip is ridiculous.You can just as well buy a car for the amount charged.