For duplicate bill

The invoice information for retail and online stores is at:

Viewing & Changing Orders - Shopping Help - Apple

View or Print Invoice

"Once an item is shipped or picked up, Apple will create an invoice for your order. To view or print your invoice, go to your Order Listing page and select an item to go to the order details. Then, select View Invoice at the top of your order details page to access your invoice.

If you need help viewing or printing your invoice, speak with an Apple Specialist" Telephone numbers --> Contact Apple for support and service - Apple Support

I would provide links and telephone numbers but they depend upon the country settings you are using. It is best if you just go to the document yourself.

If you bought your iPhone at Apple Online Shop, contact Apple directly using this link:--> Contact Apple for support and service or use this link (at the last section "View or Print Invoice"):--> Viewing & Changing Orders - Shopping Help

In all other circumstances (Apple phisycal Stores, Authorized Resellers, who have their own accounting system) contact the seller and ask for a copy of that document.

Regards

Giulio