Poor experience at Hyundai Pinetown!

Hyundai Pinetown! I took my car for a service special of R799 in August. I was called and explained that there were a few things to do such as violent refill, etc, that is not covered in the standard service. I agreed to a total amount of approximately R2600 including vat and Labour. However I had to pay a total of approximately R3100 when I had gone to pick up my vehicle. I had queried this upon going home. Eventually after weeks I was told by my service attendant Nash that there was a mistake made on their side and the next time I bring my car in they would "bump off" the money owed to me. I declined this offer as I wanted a refund for the discrepancy. We are approaching November soon. I called the manager Ryan 3 days ago and still have not received my refund or feedback, I have probably spent more money trying to contact Hyunday for months. This is absolutely poor service for such a big company, especially when the discrepancy was because of a mistake that an employee made, which the customer now has to pay for. I would appreciate some feedback ASAP from Hyunday South Africa. I would NOT recommend going there, rather go to a company that is transparent. I've always used Hyundai, but this experience at the Pinetown branch was a first and LAST!