did you move recently? If so...
I had problems when I moved from the US. Everything should be the same address (or country), the address you may have to enter when ordering, the contact address in your
UO account management and the credit card has to be of the same country. And of course you must also be in that country (they seem to check your IP, to avoid that some homeless bum from Boratville in Kazakhstan orders gamecodes with a stolen CC).
Took me a while (and 3 different credit cards) to figure that out.
If not....doh!!!
p.s. that applies if you use the OSI gamecode site. I assume you're trying to buy stuff from there.