Hmmm, good question. I am not sure. I would think you cant, as you never recieved the money in the first place.
I always thought in order to use a deduction, we had to have the money to spend, not just not get it.
Kind of reminds me of a question I asked my accountant when I first started up. I sometimes offer new clients a discount, and wanted to know if the amount of the discount would be deductable. She said no, technically not. There is a way to include it in my bottom line, but it would have to come out of somewhere, so it would have ended up being a wash. I wonder if this same thing would happen for your situation.
Whats the answer from those that do insurance billing?