This is where you calmly say, "Had you simply written down "rear wiper streaking", BMWNA would have paid you for it- and I'd have given you all 5s on your survey. Yes. the wiper broke- but you cannot say if it was abuse or broke due to a material weakness. You chose the path that would result in more money for you, since BMWNA's reimbursment to the dealer is very low for this- BUT, you choice has resulted in my feeling you are not a business that I would want to revisit."
be calm, DONT PAY THEM FOR IT. Rub their noses in the fact that they chose this path for really no good reason.
If you already paid it, nevermind- you willfully bent over for them....
Keep it as simple as possible...but no simpler.