While checking out and filling your address details you need to click on the 'Keep me Updated' tab and put your preferred email address to receive an order confirmation, order tracking and delivery docket/invoice. Refer to the screenshot attached below.
If you still have any issues in retrieving your order confirmation details, please contact COS customer service on 1300 614 133 or via email on parentportal@cos.net.au and they will be happy to assist you.