I was trying to buy a game on Steam a couple of weeks back using my Maybank card, and it too was getting declined.  So I called up Maybank.

And bad news, bro.

Maybank Management has decided to block ALL credit/debit card transactions to gaming websites, foreign exchange transactions and gambling sites.

This started in August, although I was still able to buy a game off Origin during the last week of August.  And I was also able to buy from Green Man Games just the other day.  So it seems Maybank has only been able to block Steam and Battle.net for now.

Probably you could bypass this rule by using your card through Paypal.  This could probably work coz when Paypal debits your card, it will show as a charge from Paypal, not from Blizzard or Battlenet.