An e-mail is on it's way but I wanted to speak to them to ensure they fully understood the changes I want. You know how it can be sometimes......
After I had my original invoice for my allocation, I needed some more camping and entry tickets.
I sent the invoice back with my credit card number and a covering note requesting the extra tickets. They added the extra tickets and charged my credit card for the additonal total.
Then.....I needed even more camping and entry tickets, so I e-mailed the ACO.
Three days later I received in the post an amended invoice and request for payment for the extra tickets I had e-mailed them about.
So....the ACO ticketing girls are attentive and are complying with my (admittedly awkward) requests without protest.
No complaints here.