I tried purchasing some points recently using my EON Card, and it's working fine.

Maybe you can call your bank up and ask them whether there are any transactions from the Xbox Live service.

I suffered from the same problem with the PSN. Apparently, the bank did not approve the card registration to the service because PSN charges 10 cents to the card to determine the validity of the card. In my case, it's not until I give EON a call.

If that still doesn't work, there's always PlayAsia or your local game shop.