No you don't (I don't work at a VW dealer). Your individual dealership may offer that service (why?!), but there's no legal framework that states that.
Unless you have a copy of the advert, which states clearly that it was a 300 model, then you're on a hiding to nothing here unless the dealer has a sense of honour and integrity. It'd be your word against his in court, on the balance of probabilities. You may get lucky, but you may not.