Sounds ridiculous, I'd be getting in touch with Ford UK to see if they can get something done.. I'd be looking at my rights as well, because you wanted and paid for Bluetooth and have gone above and beyond what's expected of you to let them rectify the situation, so I'd expect you have a rather good case for rejection of the car if it got to that stage.
Just keep a note of how many times (date/times) that the car has had to return to the dealership for them to look at it.
Cheers,
Grant