debit card debited without permission or knowledge

We had gone to Bidvest in Sandton to inquire about renting a car for the weekend without a credit card, we were told no, but that a plan could be made. We entrusted the sales agent (Ricardo) with our information and signed a contract that stated we pay R1600 in total for our rental, (in which we paid cash, as advised by said sales agent) and if there was a charge to our card, it would be reversed. At the end of this month our account was then debited of R2000 and on our statement it said " Bidvest online purchase" . I have been disputing this to no avail, as i have been told there is no proof that we had paid the R1600 to Ricardo (Sales agent) and that the amount debited was in fact for our rental, without there being any documentation available that we signed for this R2000. Maybe this is our fault in part for trusting a ********* word. But to not be acknowledged by management or be refunded our money is disappointing and infuriating. I am at my wits end. Such bad service and communication.