Can anyone assist with the persistent delays at Amazon's Doncaster (LBA4) fulfillment center?

I shipped 2,000 units which were delivered on April 4th and only checked in on April 13th. Initially, I was informed there were no discrepancies, yet suddenly 1,400 units are now missing. I opened a case with Amazon, only to be told the inventory was never delivered, despite clear delivery confirmation.

Now, I'm experiencing further delays with additional shipments still waiting to be received.

This level of disruption is simply not sustainable for my business.