Interesting story and I wish the OP luck - sure looks like he is due something from BMW based on the in-service date of the car. That whole thing seems VERY fishy to me.
But one part of this story makes no sense to me at all. Regardless of how the serpentine belt is damaged, HOW could debris from it end up in the oil?? That makes no sense at all, the serpentine belt is entirely on the outside of the engine driving the accessories and in no way in any contact with the oil that I know of. I suppose it could be sucked into the intake somehow, but then the debris would have to get past TWO filters to actually enter the engine, and even then it is unlikely that anything would get into the oil sump.
'11 328! Touring - Tasman on Chestnut, 6spd manual, factory upside-down "i" option