Sent iPhone off to be traded in and got lost

I recently got a new iPhone in December so I went to trade in my old iPhone. I followed all the steps and took my iPhone to aus post were they scanned the barcode and packaged up my iPhone to be sent out. Just about a month later apple haven’t received my iPhone and have cancelled my trade in. I had called them when I had the receipt from the post shop telling them the tracking as I had gotten a warning email saying my trade in was about to expire. At the time they said it will be fine and that it’s on its way. I have now lost the receipt and my iPhone still hasn’t arrived to them or been sent back to me. I don’t know what to do.