FBA SHIPMENT PROBLEMS

I have a shipment that Amazon shows discrepancy when receiving; however, the items say “Investigation completed – shipment contents counted and confirmed”, but were never added to my inventory

When i try submitting documentation im receiving an error and when i open a case Amazon says they have no record of receiving the units. (Contradicts the status listed on the contents page when viewing the shipment)

Any recommendations on how to get reimbursed for this type of issue? Or any preventive measure I can take to avoid similar issues in the future?

Thank you in advance!