I don't like being charged for an oil change when ...

I don't like being charged for an oil change when we had an agreement once we purchased the vehicle that maintenance would be done for free. So when the oil change light came on at around 5000 miles, which is typical, I wanted to get the oil changed. But I was told that I would have to pay for the oil change because the free oil changes were set up every 10,000 miles because synthetic oil is used in the vehicle. I had no knowledge that the oil changes were not done every 5000 miles and there has been no communication since the purchase to that effect. I'm not a happy customer because of this situation and I hope Mike Johnson reads this message from a disgruntled customer!!!!