Helped need- shipment delivered almost 80 days but never 'checked-in' or 'delivered'

We have shipment delivered to DUS2, Germany on 26th Sep, nothing checked in, waited a month and shipment closed, now waited another month, 36 Days later shipment is closed.

Seller support is still useless by telling us to wait for 'shipment to become eligible for investigation' . Apperantly a shipment can only become eligible after it has entered receiving status which ironically has very little chance to happen.

Thank you for anyone can get us any suggestions on how to resolve this!

Shipment ID FBA15J9K3YSX

CASE ID 10504263352