Hertz Cape Town poor service

We made a booking prior to the Easter weekend with Hertz Cape Town. The booking was accepted and payment made. On arrival at Cape Town International airport, Hertz informed us that the booking was rejected. We requested to speak to the manager who offered no assistance just merely saying sorry the system rejected the booking. No effort was made to try and make alternative arrangements. Apparently the system allows overbooking and then later on rejects confirmed paid bookings. We were left stranded with 2 small children. Whilst at Hertz another fellow customer had the same happen to him. Being Easter all rentals were booked out and we had to make use of a taxi which did not have any baby seats. Best of all is, 14 days later we have still not been refunded by Hertz.