If an electronic check payment was accepted and processing in ASAP in error, you may still have the ability to cancel it if you have access to your payment gateway. If the payment has not settled, you can log in to your payment gateway to cancel the payment directly with them. Here's a support article that details how to do this as well as the information you'll need to provide to us in order to update ASAP to reflect this information.
Cancelling Credit Card/ACH Payments