I really should keep out of this as its not a technical issue and I obviously come from the other side of the fence.
When its busy communications get strained. I was given keys to a Saab to align last week, went to one in the parking lot and the key was a little rough (Saab ignition is on the floor and they are POS). It did work though and I finshed the alignment.
Wasn't the right car! Of course we didn't charge for it. You obviously shouldn't be charged for something you didn't ask for. BUT, you set up the circumstance by asking for unusual procedures and a mistake was made.
If the situation was in my hands I would write off the oil change and pay the technician. He did the work and there is no changing that. I would do it with a smile. But my mind would not be smiling. If I let the human side take over that small event would cost you if return business was the plan. It may only cost you my interest in your problems, but that can be way more in the long run.
In the long run we are all people. If such an event occured in my shop and the customer said nevermind, he would benefit greatly. Such a small gesture (make sure to point it out) can be worth a long term fortune in that most important of relationships: customer-business. Get an up on that relationship and it will be a happy one.
Personally, I would note the issue and see what they do. if they offer to take it off, say nevermind with a smile. If they fight too hard its your call how to proceed.
Bosch Master, ASE Master, L1
33 years MB technician