Canceling an Invoice would imply Canceling the Service you had ordered along with it. However, note that you can cancel only those Invoices for which you have not paid.

To cancel an Invoice

1. Login to your Customer Control Panel. 

2. In your Control Panel point to My Billing and then click Pending Invoices & Debit Notes.

3. In the list of Pending Invoices, you can select the Invoices you wish to cancel and click the Cancel Button. In the next page, you will be asked to confirm the Cancellation of the Invoice and the action associated with it. Proceed after confirming the same.