you will never be able to claim on the warranty, unless you buy from VW. especially as a load of these units were stolen a few years ago.
with current serial numbers i think thats unluckly

As stokeballon has said, i done the same, mint condition and ebay seller has his own warranty included, and has replaced mine with a Brand New unit,due to Refurb having incorrect motherboard installed making it not sync with my Multi function steering wheel. Even a plastic protector on the screen with VW Warranty sticker seal untouched .Mine was 6 months old when it had a fault, and it was fully replaced by the Powerseller on ebay no quibble.
Doesnt mean when you spend over a grand on one 2007GTi like you did, doesnt make all others on ebay for half that either stolen and some cases Refurbs with no warrantys.

Feedback from fellow forum users is your best bet to find best seller with good History, rather then looking at sometimes corrupt feedback info stats on ebay itself.