AutoNation Chevrolet Gilbert

I took my Yukon for an oil change and the price in the service area was for $99.00 for an 8 qt oil change,When talking wiht the service rep he advised me I needed 10 qts due to having a 6.2 litre and there would be an additional cost of approx $20.00. I paid the bill and picked up the vehicle and once I arrived home I looked at the bill and the vehicile only took 8 pts not 10 as advised.Called service to discuss the overcharge and was sent to service manager voicemail. I left a message regarding this and my call was never returned. I will not go back as not only was a scammed out of $20.00, they did not even return my call. The GMC dealer was $89.00 for the same service on a 6.2 right beside them in Gilbert when I called to inquire.