You are correct. You must call your brokerage to repair it.
I've had this problem a few times. Calling my brokerage (Ameritrade), I told the representative that an apology wasn't enough, that I wanted some commission-free trades. He happily offered ten or fifteen and I doubled the number, figuring he could counter with something more reasonable. I made out like a bandit and the broker was glad to clean things up.
You won't have any trouble as this is a brokerage responsibility. You should not be going elsewhere to resolve it as only the brokerage is positioned to manage this issue.
Good luck!