I think DTD are wrong. They just 'organise' the deal, the contract is between you and the Dealer, wherever in the UK they may be.
As always, check the Finance agreement carefully before you sign and unless it mentions paying back deposit contributions & sweeteners within a certain time, then you're fine.
You have the RIGHT (UK Consumer Law) to withdraw from a credit agreement within 14 days. Day 1 is the day after you sign the finance paperwork which should be the day you collect the car. Interest is charged on a DAILY basis, and once you withdraw you have 30 days to settle the balance with VW Financial Services. The balance is frozen from the date you withdraw. One snag is that once you withdraw, you can't go back to the credit arrangement so ensure you have the funds in full to settle it.
I've no idea if VWFS will still offer it, but I got 2 years servicing for £199 (1 minor and 1 major service) which I think is good value as I paid over £200 for a minor on my Mazda. If you're not offered that by the Dealer - its worth a mention.