If you're referring to purchases you've made in-game using Diamonds, Coins or Battle Tokens, this is the correct article. If you're referring to purchases made with your credit card, please follow this link.
During the development of the game, we took measures to ensure accidental purchases are avoided. The most noticeable measure was the inclusion of a confirmation button to make sure that you validate any in-game purchase made. However, even with this feature, we understand that accidents can still happen.
The above being said, unfortunately, our support team is currently unable to revert any in-game purchases. We apologize for any inconvenience, and we hope to be able to provide this service at some point in the future.