It could be argued that before VW AG has locked in a build date, the contract isn't rock solid, especially if the contract as drawn up has a date of fulfillment (delivery) that cannot be assured. Unlike most car manufacturers that have a short lead time before building (typically 6 to 8 weeks), the dealership will be waiting an age for VW AG to finally confirm your build week. My contract states fulfillment by the end of March 15, so mine's been breached, but what are you going to do when you know the car will come (eventually) and your p/x is fixed?
Whatever the legal fine details are (a contract for something you ordered face to face, that is available almost immediately, or at least with a reliable fulfillment date is solid), i've never known anyone here on the other forum duck out of their order because of the extended lead times and not get their deposit back.
They don't seem to be going out of their way to encourage return business by screwing you when they've not lost out at this point. Always be polite when asking (it always helps keep things smooth and stops them going out of their way to inconvenience you), but it might be time to publicly ask VWUK via their facebook page if they can intervene as you cancelled your order due to lack of faith that they could deliver within your expected timeframe. Be polite, but make it clear that the order hasn't progressed past stage 2.
So why are you cancelling (just asking to understand your situation better)?
You realised that you could get more off the car elsewhere?
Lack of info from the dealership or lack of faith for lead times?
Change of mind for the car, either you don't want a new one or you don't want a VW any more?
Something else?