Cancels a scheduled bill payment.
This function generates the Signon and Payment Cancellation request page, submits it to the financial institution via secure HTTP Post, receives the response, and parses it.
The PaymentId parameter identifies the payment to be canceled. This is the id assigned and returned by the server at the time the payment was scheduled (that was stored in Id).
The following properties should be set when this method is called:
Upon successful response, the server will return the Id which echoes the PaymentId.