As Paul rightly said, they took the part ex off me back in May so they could still honour the part ex value that they'd offered me on the previous car I ordered, that they subsequently sold from under me!!!!! Anyway, thats a different moan. I handed over the part ex and there was no mention of a lesser value + a discount for the S3. It was/is all written as Part ex. Seems pretty cut and dry to me but they are trying to say that it was divided up into part ex + discount. The part ex value they're offering is less than todays book for it, and was considerably less than book in May. There's no way I would've shook his hand to that deal, not with my luck!!!
I've sent them an email listing their options to settle this matter (one of hich is to return my part ex, thanks Robin!!!) and am still awaiting their response. I'm off to Chicago for a few days now so I'll give them until I get back then it's war!!!
I've had the worst year ever when it comes to cars. Fingers crossed that next year I can get rid of my money with more success!!

Thanks again for everyones input. I'll let you know any developments (and if I need that lawyer!!)