You will receive your order's invoice from us via e-mail immediately after paying for your order. If you lose your invoice, you can always download the invoice from your account. Log in and click on "My Orders" and then on "View order". Click on "Invoices" (next to "Items Ordered") and click on the "Print Order" button (top right). This probably means you placed your order quite recently, and it hasn't yet gone through. In that case, wait till your order is shipped. The button will then automatically appear.
Did you place your order as a guest? Please contact us for a PDF of your invoice.