Will, the dealer is bluffing you, he’s already given you his first answer. I called mine and he said to me he will ask his manager and I was only on hold for a min or two. Processed everything over the telephone. Regardless, if mine had refused, I still would’ve headed down to Marshalls Hampshire (2 hour drive).
It’s a sales technique. If I was in your position, I would cancel and reorder but secure yourself a deal with another dealer that will honour it. Only difference of price from Q3 to Q4 is a £50 increase on the 320i.