Flushing engine amount

I booked my vehicle for service and was told major service it will cost me R2499 which I was okey with it, thinking that everything its included in it. There after 2 hours while I was at work was called to be told to flush the engine oil it will cost me R330. Which I did not understand as it have to be included overall as part of the service. when I ask the lady why I was not told about at first while I was there, because everytime when I take my car the engine oil have o be flushed and refilled.

The lady rep**** and said " Mam, flushing its not part of the servicing. Which I did not understand and her attitude of not wanted to listen to what I have to say. I did not like it. I ended giving authorisation even if I was not understanding it.