write into a car mag.
i did that when i had heaps of teething problems with my MINI and after 11mths they agreed to completely replace the car... co-incidently one week after my letter was published in Autocar...
What Car is good for this too, they have a dedicated section on this. They often help you to contact the manufacturer.
Given the Golf GTI is so new, this will be "newsworthy" so I would expect mags to take up your cause.
If still no joy then escalate to VW HQ and also Trading Standards.
Best of luck.