Guy made a mistake - big deal, no need to be hostile.
Go and tell him he made a mistake, if you want the CD Changer ask him to get one fitted.
If you don't want it then just tell him that he made a mistake and its obviously not what you were expecting - but a full tank of fuel will make you forget about it.
Edit : Any reputable Garage will accept this as a mistake and do whatever it takes to rectify it./