You can see your invoices and billing history by selecting 'Settings' then 'Invoices' in your FeedbackExpress account.
If you need to access or print your invoices you can access these very easily. Previous payments will be listed here and you can view an invoice by selecting the appropriate row and hitting the 'View invoice' button. These invoices can then be printed off as you need them.
FeedbackExpress will also email you each time a successful or failed payment attempt is made.