Shocking service and high price

The service I received from Kia East rand was shocking. I missed my maintenance plan by 1000km, and was informed I would have to pay and was assured they would keep it to the minimum since I would be paying. The minimum fee came to R4200. I then received an sms advertising spring madness special R850 for basic service. I phoned and enquired about this and they stated this was only for the KIa Picanto and not the Rio. They then stated they would give me a discount on labour for R3700. Prior I had a call from a male at Kia saying that I need to get my windscreen plugged for R250 which I assumed would be included in the R3700. When arriving to collect my car I was presented with the invoice for R4100, I enquired about the price, and they said that it was for the windscreen. They stated that he does not work for them but they are billing on behalf of him? And he stated he was from kia. as a single women I assumed this was necessary to keep with my maintenance plan to not get penalized. On returning home the one thing I requested on my boot I found was not fixed. I think this price was shocking and I feel they are false advertising! I will be using another KIA from now on!