Amazon lost my FBA item

Hi!

In one package, I shipped 5 books. Amazon told me they did not receive one of them (the most expensive one), it did not have a barcode, just the ISBN. I went to file an investigation request, but the system was not allowing me, saying they already invested it. I contacted them and this was their email response:

Thank you for getting in touch regarding your concern.

We comprehend your concerns regarding the discrepancies within the Shipment ID: FBA17Hxxxxxx for ASIN: 0803xxxxxx.

We greatly appreciate your effort for providing required documents to investigate the issue.

Before we proceed further, kindly accept our sincere apology for the inconvenience borne by you.

Upon checking, we see that the units are marked as “Investigation Completed – shipment contents counted and confirmed.

When we receive shipments with quantity discrepancies, we automatically initiate an investigation on your behalf for the items in your shipment.

As part of this investigation, we perform a second, physical count to reconfirm the quantity of the items received. Items are marked “Investigation Completed–shipment contents counted and confirmed” when we have completed the investigation. We have completed an additional check in response to your request.

We have no record of receiving the units in question. We regret to inform you that this particular reimbursement request you made cannot be processed.

Kindly accept our apologies, as we understand that this may not be the response you would have anticipated.

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What can I do now? How do I respond to them? Send them images of the items and I placing them in the box that was shipped?

Thank you.