The diff requires an oil change too. 3 years or 30k miles, whichever comes first.
Personally, I wouldn't be overly worried if the car looks well otherwise. The oil is longlife and can last up to 20k. In the two services it should've had, the main thing other than the oil change is just looking over the car for anything broken or falling off. Or minimally worn brakes that they can convince you need replacing.
Provided they either fully service it or give you an equivalent discount so you can take it to a VW dealer for them to do, I'd say go for it. The cars seem generally robust and reliable. So I don't think you've been stupid or made a mistake 
On a more positive note, what's the spec?
Getting a vw dealer to do the service also has the benefit of software upgrade check since there is no service record. My 7.5 required a software update to cure a stop/start problem. Might be worth going for the discount if they are willing?
The diff requires an oil change too. 3 years or 30k miles, whichever comes first.
Personally, I wouldn't be overly worried if the car looks well otherwise. The oil is longlife and can last up to 20k. In the two services it should've had, the main thing other than the oil change is just looking over the car for anything broken or falling off. Or minimally worn brakes that they can convince you need replacing.
Provided they either fully service it or give you an equivalent discount so you can take it to a VW dealer for them to do, I'd say go for it. The cars seem generally robust and reliable. So I don't think you've been stupid or made a mistake
On a more positive note, what's the spec?
Great point guys thanks. I've called them and asked them to cancel their "service" (which was a healthcheck and oil + filter change) and they've knocked off £200 for me so that I can go to VW. It's still under warranty so I guess that'll come in handy when I take it for a service.
They also said they're going to try and get in touch with the 1st owner again and see if they'll get any info on the garage it was last serviced at (which I highly doubt).
Hopefully they'll find something, but as I'm expecting to have this car for 5-7 years, I think the first 2 and half years of missing service history will be okay.
On a more positive note
specs are: DSG, 18-inch wheels, tartan seats. Got all the gadgets I've been looking for (lane assist, parking camera, keyless entry). Is in great condition minus a few dents which will be fixed, very clean, and nothing felt strange when I took it for a drive.
