Thank you for your supporting S3Drive !
Your support item made us review our checkout process and in fact auto-receipt wasn't enabled.
We've fixed that this morning so these details are available on the account page, but it will only apply for new subscriptions/license purchases going forward.
I've sent couple last receipts manually, if you haven't received a receipt by now, can you please PM me your e-mail, so I can make sure its sent to you? (edited)