Over charged for rental

Rented a car from Port Alfred on 25th July and dropped off same day at PE airport. They did not send me an invoice but I noticed they did not refund me the full amount. When I queried this they advised that I only returned the vehicle on 28th July which is not correct. I reported this issue on 5th August, no-one has bothered to call me, it has been going back and forth by email with the customer care team and they don't seem interested in resolving the issue. I eventually got hold of the Agency Principal at Port Alfred this morning and she already confirmed the error and has requested a refund for the two days over charge