Please help, I'm confused!

Around a month ago shipment - FBA15J8WNCL6 was received and checked in, it them moved into FC transfer and was heading to tilbury.

During this time units were prime eligible with a 3 day shipping time (completely expected for units in transit).

I queried the delay but was told units were still sellable and I had nothing to worry about.

Then they left FC transfer status, but still had a 2 day shipping delay.

All units are now showing out of stock with 0 sellable. I queried with SS when would an investigation begin, I was told there are no lost events, and there was nothing they could do. Even though all items have been delisted, during this time a customer ordered a product, and the transaction was cancelled by Amazon presumably because the unit could not be located.

Where do I go from here please? I have another £500 shipment ready to send in but I want to make sure lost items will be investigated and reimbursed before I send anything else in. This is my second lost shipment (out of 5) in the last 4 months.