Welcome to the fabulous world of Volvo and their legendary evaporators, which magically make any refrigerant you feed them disappear. This is a hard call, but any reputable, conscientious dealer would have suggested that you have the system checked for leaks in the system and not simply re-charge the system. You can go back to the dealer and raise a very polite ruckus about it, and see if they will do anything. You can be really nasty and have the work done, pay for it with a credit card and then dispute the charge, but as I have never done this I can't recommend it. Just a thought. You can call Volvo headquarters and bitch to them. If nobody helps you, make a sign and picket around the dealer's lot this weekend, maybe that will get their attention.

Bottom line is that this leakage argument of theirs is BULLSH*T.