Never assume that after you THINK you have requested something from an organization or venue that it will happen. Make sure you think about all of the logical steps that someone would require of you for a specific event, and ASK QUESTIONS.
It almost never works out to look back at an event and negotiate changes in pricing for something you thought was clearly set and understood by both parties.
But, even though it is frustrating, continue to give great customer service and keep a clear head. Don’t get heated. Don’t assume.