According to Apples Returns and Refunds policy below the iPhone will likely have been required to be returned within 14 calendar days.
Returns & Refunds - Shopping Help - Apple (AU)
Apple Store Returns Policy
You can return your items to an Apple Retail Store within 14 calendar days of receiving your order. You need to bring a government-issued photo ID and confirmation of the web order number with your items.
Standard Return Policy
Returns are subject to Apple's terms and conditions. For iPhone returns, please refer to the iPhone Return Policy section below. For eligible products, you have up to 14 calendar days from the time you receive your item(s) to initiate a return.
iPhone Return Policy
If you are not fully satisfied with your iPhone purchase, you can return your undamaged iPhone to the Apple Online Store within 14 days of purchase for a full refund. Please check your Order Status online or call 133‑622 to request a return. The iPhone must be returned in the original packaging, including any accessories, manuals and documentation. Please note that returning your iPhone pursuant to this policy will not automatically cancel your mobile network agreement. You must contact your mobile network operator to cancel your mobile network service. If you cancel your mobile network service, you will be responsible for all applicable usage fees, prorated access charges, taxes, surcharges, or other charges imposed by your mobile network operator through the termination date, including any early termination fees or penalties, if applicable. Please contact your mobile network operator for more information about applicable fees.
This section provides the instruction regarding the lapse of time that you can return an iPhone.
...you can return your undamaged iPhone to the Apple Online Store within 14 days of purchase for a full refund...
As always this may vary from region to region and I would highly recommend contacting an apple support representative regarding your return.