NEW ON AMAZON and would like some help about triggering a new case log for missing returns from AMAZON

Hi ive been employed by my company for 2 months
So getting to understand about amazon has taken time for me/

The problem i have found is that i cant get a trigger a new cas log.

the problem is when a customer returns an item back to amazon, amazon will create a shipment back to our office. I have the tracking number from them but it is not available. This returns was created on for sept 19, two for sept 10 that we have not yet received . Typing down the tracking number on royal mail and it doesnt even come up. The item hasnt been reimbursed as i have checked.

Please could anyone give me some advice on how to trigger a new case log as im a newbie.plus the question is how long do we have till we can submit as im worried at it was for 10 sept and 19 sept.

kind regards