Of course you're not being unreasonable.
Even if you were misinformed, a normal person would have told you what you DO need to do, not rudely dismissed you like that (and found out if she didn't know - it's her bloody workplace whose stamp you need after all).
I would have asked to speak to a manager and dropped the rude cow right in it. I have very limited experience of BO's (and only through friends) but my 1st impression was that many staff appear to look down upon the people they're supposed to be helping.
How did you leave it ?