Bluechain users can cancel a pending payment. However, once a payment has been completed, it cannot be cancelled.
Hover over the pending bill that you want to cancel
Click on the bin icon that appears on the right-hand-side
From the popup message that appears, click Yes, delete to confirm the action
Contact support by emailing [email protected] or by using the chat box on the website immediately, as they may be able to help you cancel the payment