Google produces an official invoice statement once per month, which includes a detailed history of all account billing activity that took place over the previous month. 

Any charges to a credit card during won't show up on an official invoice statement until the following month.

Google usually releases the invoice statement documents for the previous month's activity after the 5th businses day of the following month. Once produced by Google in a downloadable format, OSiM will email this official PDF to you for your records.

If you require a proof of payment sooner, you can log in to view your Billing Activity page with your invited Google account anytime. This page logs each transaction, including costs and credits, so you can view individual payment receipts and screengrab the images (not available as downloadable PDFs).

Note: Current month numbers aren't updated by Google in real time on the Billing Activity page.