I understand your frustration and had the same thing happen to me, only the bill came for AH the day I got a BFN, so I was even more upset and frustrated. Sure enough, when I looked at my paperwork, I had consented to AH if needed.
Later, in talking to the RE and getting a game plan for round #2 (which did work, by the way - we did a 3 day transfer that time), the RE said that AH is routinely used on Day 6 embryos. In our case, with that first round, we also did not have blasts at Day 5, whcih is why we were pushed to Day 6.
I hope this cycle works for you! Hang in there!
As an aside, it's always a good thing to scrutinize your bill. With our second cycle, we were charged for AH, even though it was not used. I called and got it straightened out, but only with the intervention of my RE, who confirmed that AH was not done the second cycle, even though the paperwork stated that it had been done.