Sylon - I would go back to the dealer and ask for a new set(parts warranty). I replaced my wiper last year, and I really like the BMW ones. I even made a DIY. I suspect you either got an old wiper set or the tech who worked on your car put the new wiper blades on his ride! Don't laugh... it happens.
The BMW wiper blade set is: BMW part #61610420549
The wipers are 500mm long (20") blades. I think
I paid like 40 euro for them. Any Bosch wiper blade set should work as well. But you should be able to get another (free) set for your local dealer.
Fyi... here is my DIY...
DIY changing your BMW wiper blades…
http://www.1addicts.com/forums/showthread.php?t=472014