Missing FBA Pallet Shipment

On the 6th March Amazon took delivery of a pallet from us but, after 100+ days, the shipment is still listed as "In Transit"

We've raised several support cases and provided every document requested, including the signed delivery note, but the response is always the same; "we’ve determined that this shipment is not yet eligible for reconciliation".

We're clearly stuck in a loop where Amazon won't investigate until 60 days after a shipment checks-in - but that'll never happen because they haven't checked it in.

We've spoken to several support representatives who have promised to investigate ... then we get another automated email telling us it's "not yet eligible for reconciliation".

Has anyone else managed to resolve a similar situation? - I feel we're just going round in circles now.

Any suggestions gratefully received