I'm confused. How did this happen? Did you wake up one day and your agent was sitting there holding the house open? :D
I guess I'm a little surprised your agent didn't tell you they were scheduling open houses. Usually, the agent would WANT to tell you they were doing open houses as that's a GOOD thing, unless you specifically said you didn't want any open houses. And, did you not know because you don't live in the house or you were out of town when they were being held or what?
Hopefully, your agent has sufficiently apologized. I hope the agent's motivation was just to get your property sold, and the open house was a means to that end.
Let us know how this works out!!