Blaming the customer for mistakes

When receiving a written quote and a quote via e-mail from the Multifranchise in boksburg I then paid the required amount and requested that the part needed be ordered. When collecting the part which costed R6498 it was noted that the incorrect part was given to me. Now I am told that I need to fork out a further R2999 in order for the correct part to be ordered. Their staff cannot place an order correctly or produce a correct quote and the fault costs me money? After being told by the parts manager that I will not incur further costs, they get the service advisor to contact me and inform me that I will need to pay the difference for their mistake? What kind of service is this? And they expect people to bring them business and buy their cars when they cannot provide after sales service to their clients??? Absolutely pathetic.