The track fill requires a couple of hours of extra work to access the top fill port on the transmission. Did you ask the dealer to do that? If not, it's highly unlikely they really added 12 quarts (or liters) of DCT fluid. You may have gotten ripped off.
(Yes, I know you can raise one side of the car to add extra fluid through the side fill port, but that's not a GM approved procedure and not something a dealer is likely to do. Especially not if the owner didn't ask for the track fill.)