Please follow the guides as below:
1. Login to tw.battle.net. Click on Balance and select "Buy balance".
2. Enter the amount you want to redeem (Example: put 100). Click "Continue to Payment" to proceed to next page.
3. Please choose payment "MyCard". Click "Pay Now" to proceed to the next page.
4. Click "Continue to MyCard" to the next page.
5.Choose "MyCard Points (點數卡)"
6.Enter Your MyCard code and pin, click redeem (進行儲值).
Please click HERE to buy.
TW Battle.net Official website: https://tw.battle.net