Wrong product no refund

General Motors witbank sold my wife a wrong lock set and told us it was the right set for the car that we took there to show them. We took the car elsewhere for fitment of the lock set and the guys there lost the packaging and after a week told me it was not the he right lock set for the car. We then tried to take the lock set back for a refund but were told that they won't take it back as it did not have the packaging. My 2 question to them are 1 - What must I do with the lock set which cost me R3500?. 2- Is this the attitude they give to their customers because it shows incompetency from their side. How is it they prescribed the wrong lock set. Did they just do it for the money ? I would appreciate if they could get in touch with me to explain this lack of service.