Have you tried getting p*ssed off with VW customer services? That's your next phone call. After that, I'd be inclined to suggest to VW that you'll get an RAC engineers report on the unit, and look to some sort of partial meeting of the costs. After all, it's widely held that in cases of Teves ABS faults or aircon compressor snafu, they generally stump up if there's a full service history and the car's less than 5 years old.
Don't back down.