A very important point:

I tried this and am in back and forth emails now trying to get a refund.

Evidently the playspan store can only redeem purchased diamonds on United States servers only. The international set of servers, regardless if they are the english speaking ones or not, will not work. At least not at the moment I tried.

There is no information telling you this, until after you finalize your purchase, then hit redeem and it brings up the Runes of Magic account login, where in it only displays the United States servers.