Stock delivered to Amazon UK but zero showing in SC

I have a client who sent two shipments to Amazon UK in August, both tracking shows delivered and signed for but we're seeing nothing in Inventory. In the shipping queue it doesn't even show that it was in transit, delivered etc just that the shipping plan was created.

Going round in circles with support. First they said it just needs to finish reconciliation, now they say the number of units received doesn't match that in the shipping plan, which simply isn't true.

It's not a new account and they haven't had any issues like this in the past and still using the same carrier. Has anybody ever had this issue before?