I needed one, too. Two month ago.I never got a proper one.The sent my a receipt, but it was full of mistakes (date being the beginning of the contract some years ago, not for the actuel billing period or the payment). And it was only some text in a mail, not adocument, not even a logo.
They did sent this mail quite fast. But I didn't noticed it, because I was waiting for a mail with some attachements.
Some weeks later I noticed the answer and after printing etc. I noticed that it was screwed up concerning the date etc. I did sent another mail but I didn't got any answer for 1 week now.
What kind of company is this not able to sent you proper invoices?
I love the CMS, but I am really a little fed up with this invoicing issue. My experience tells you not to expect to much.