You were talking to a Tier 1. There's no refund you're getting. Go read USCIS website itself.
And I believe you're supposed to be mailing that I-824. Field offices don't take applications. Again, you got wrong information from Tier 1. The letter you got tells you how to go about it. Follow it, just like you did with the I-485.
Well, since you got an appointment today, be sure to give us an update about your field office visit. Maybe there's some new USCIS policies we still aren't aware of.