For every purchase you make on the website, you will receive an invoice (in PDF format). You can find your invoices in your account at Payments. You can adjust your billing information in your Account Settings. 

You can find an overview of your credits in your account, in the payment overview. Here you find the purchases of credit bundles and payments made with credits.

Please note: when you've purchased a promotion it will become active once you've placed the advertisement online.