Hey Kalvan! Thanks for the advice. Unfortunately, your solution didn't work however. When I changed it to US, it said I needed to pay 20 dollars (like it should), but it also said that there was only $18.75 on the card, not $20.00
It's been awhile since I've bought diamonds with UGCs. However, I seem to recall that while redeeming them at the PlaySpan webisite (after going through Recharge Diamonds and choosing the diamond package I wanted), there was a US$6.00 charge for each card. Each card did redeem for its face value, though.
Edit/update: The US$6.00 charge mentioned above, I believe, goes to PlaySpan directly from redeeming the card.