I think this is a good learning curve for everyone. Lol
Previously I worked in an event company, we have a habbit. We will write an email and send to the inolved party again, after confirming the agreed terms, changes or details through phone call. This is to make sure that everyone is in the same page and to cover your backside in case the clients play roti prata. You know, at least there is black and white.
To prevent the same thing from happening, next time after an event or the next morning can send them an email to them, to recap what are the amended terms.