Unsatisfactory Service from Hyundai agent in Witbank

We have sent our Hyundai Elantra 1.6 Year 2009 model to Eastvaal Motors Witbank for repairs as the issue we were having was the car was losing power. Eastvaal Motors changed a Pencil Coil but when we received the car back, the issue seemed to be resolved for a while then it started up again. We took the car back to them and they advised that it could be one of 2 things, Map Sensor or the Body Assy Throttle. We advised them to replace the first item and the car continued with problems and now the idling became an issue and the car would stall on numerous occasions while driving. Subsequently we then sent the car back to replace the Body Assy Throttle. Eastvaal Motors has had our car now for over a week and when we inquire about what is happening we are told that they are dealing with Hyundai SA and we get no proper feedback. All we are told is that the Line Manager would phone us but are yet to hear from him. We would like Hyundai SA to address this matter with Eastvaal Motors for a resolution otherwise this will be the last Hyundai we will ever buy as it seems that Hyundai cannot maintain their vehicles.