Its very difficult, to deal with car dealers that are highly trained not to give anything away, and some will walk away from a sale, if it doesn’t go their way. At the moment, with all the pent up demand, sales aren’t a problem. You will need to present all your evidence, and be confident, however, the dealers know you want the car, so they have the psychological advantage. Depending on your personal circumstances that may not be for you, if its not, don’t waste any more time, start looking at choosing another car from another dealer, while bmw chew over your complaint, It might go your way. In your position, I would be pushing for the original deal, less £500 which is a common discount with bmw, and leave that on the table. By all means try to push the complaint up the chain of command, but it will require energy. The problem is covid restrictions in getting a face to face meetings. The economy will be opening up in the next few weeks, make use of it, by looking at reviews on you tube etc. Be assertive in your dealings, with regular phone follow ups to track the cars progress. As I have said before, its up to you if want the gran coupe, its a nice car, but I don’t think its value for money now, my car would be near £3k AP, with tinted rears. Look at your options, a decent A class or CLk, or 320, is within reach and can be found in stock, using the brands web search.