Maybe they charged for, but didn't replace, the filter?
It wouldn't be the first time, or the last, that a stealership has charged for work which hasn't been done. I always mark parts which should be replaced, if I have to let the muppets touch my car.
I recently serviced my wifes Volvo. I changed the oil and filter, and the air filter. Despite being charged for these items at the last service, they had not been changed since the car was new. Evil creatures sent!
:flame: