To cancel your pre-purchase:
Navigate to https: //eu .battle. net/support/en/help/product/war3r
Select Request a Refund.
Select your payment method and reason you would like the refund (“no longer want this product” is recommended).
After your refund is complete, you will receive a technical ticket addressed to your blizzard account accessible next your messages at Battle .net. Please take the time to fill out the short survey and express that you are unwilling to recommend Blizzard games to your friends, and give your opinion on the situation in the manual entry box. Every cancelled pre-order helps.