Yep, start easy, softly softly catchy monkey... Go up the ladder, as you have been, let them have a check, and ask for their findings in writing (try to be there as well on test drives, so they can't say it didn't do it). If they argue or seem put out by it, tell them that your keeping a diary and file on the matter for future reference, and it is YOUR car, and THEIR problem! But work your way up the ladder, giving each level enough rope to either sort the problem, or hang themselves. Remember if not happy you can ask them to get in touch with the factory or send out a top VW engineer instead of a normal dealer mechanic, as some things are beyond their scope of experience.
A diary is a good idea, keep note of time of calls to/from people involved and all emails and correspondence ( sum it up in the diary and keep a printout in your file). Also note mileage and fill ups, and again keep a copy of receipt showing litres etc in your folder..
At the end of the day there is someone on your side apart from us. He is the last ditch person and needs as much documentation from you as he can. His name is "The Ombudsman" as far as I know ( used one to sort out an insurance claim, long story but won the day), also possibly trading standards if vehicle is not fit for purpose (doesn't behave as it should), but these are howitzers to take a simple headshot, and best kept up sleeve and all that.
Believe that it will work out in the end, and remember, your a customer with a genuine problem and deserve respect, if someone treats you differently, take names etc and add to letter of complaint.
Sorry for the essay, but good luck, and keep us all posted. From my test drive of my future T6, it will be worth the hassle to get it sorted, and why should they put you off of such a lovely motor.
