I am genuinely sorry for you, as they say a grand dont come for free!!!
Thats alot of anyones hard earned money nowadays, and i know what you are saying that you feel hard done by, they have really made a contract with you to sell it at 10,850, however if they did have it at a lower price and you could have had it at that price, then as mentioned their work ethics are all wrong, and from a big company like Audi, you would expect alot better.
I would speak to the site manager and write to Audi HO, what have you got to lose, apart from YOUR money??
I would also, if they dont give you a good response, tell them that you are going to name and shame them, i know it may seem harsh, but you asked for our opinions and this is what I would personally do.
Local newspaper, watchdog, rogue traders the lot mate.....
Good luck, i really hope you do get a good outcome on this.
Please keep up posted mate.
Nilz