Hi Mark. You can argue your case with the dealer, but they are not obliged to assist. This happens all the time in the car industry, as in other industries, where the pace of development means that cars become obsolete in a 3-4 year timeframe. Your order was placed in September and the face lifted Golf was announced in November, so it’s unlikely that the dealer would have had any information about the facelift at that time.
The flip side is usually that there are better deals available on the older models than on the brand new versions, but it’s not a given and always depends on supply and demand.
Given that you ordered the car five months ago and are due to pick it up in a few weeks, the dealer is unlikely to be too helpful. Your car will probably have now been built and will be making its way to the UK, so it is well past the point where the dealer could cancel the order from the factory. If they allow you to cancel the order, the car will still arrive and they will have to find another buyer – and presumably sell it for a lower price. That is not something they will want to have to do.