Bi-xenon is the term we throw around marketing wise for the HID lights used on the Touaregs. The term designates a system where high/low is HID, but there is still a flash-to-pass lamp that is halogen. This is the inner lamp holders we would ordinarily think of as high beams in other cars. Here, it's not!
I'm assuming you have bi-xenon headlights, of course. If you don't, then I have halogen upgrades which range from $34 to $40 per pair. Do your lights self-level from a down facing position when you turn over the ignition?
I'm a Philips lighting distributor. These bulbs are always replaced in pairs. I sell a pair for $150, freight prepaid Priority Mail within the USA. You'd need to contact me directly to order, phone me at 888-257-3882 toll free