The reference is on your confirmation, and looks like RVG followed by seven figures. We ask for the name on the booking as well so nobody else can read it.
It is in the email we sent when you booked, and in the text message if you gave a mobile number. Reception can also find it from your name and the dates.
Dates are changed by reception rather than here, so that we can check the new nights are free before anything is given up. Call and it takes a minute.