Bluechain users can cancel a pending payment. However, once a payment has been completed, it cannot be cancelled.
On the web portal
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
On the app
Navigate to the payables section of your Activity tab
Swipe from right to left across the bill you would like to cancel
Follow the on-screen instructions to delete the bill