The Apple ID does not match the one associated with the order

I completed an EDU order for a new Mac this morning. The order doesn’t show in my AppleID, but I got the confirmation email from Apple to the email address provided during the order (paid with ApplePay). That address is equal to that of my AppleID. When logging into my account from the Order Status page, I get the “The Apple ID does not match the one associated with the order”. If I then try to look for this order without logging in, and provide that same email address, it shows “The order is already associated to another AppleID”. I spent 3h today on the phone with Apple Support. I believe I’m now acquainted with every advisor from their Greece office (I’m based in Italy), yet they couldn’t help. They bounced me from one department to another, some of them feeling sure the technical support should’ve been able to align the order and the AppleID, others bouncing me back to post-sale since only they could help. In the end, all I got was a “don’t worry, Sir… it will be all right”. That’s the best I could get from them. No one was able to solve this. There are several topics about this on discussions.apple.com but none of the solutions proposed there has any effect. There is no “Add to AppleID” button in my order. Does anyone here have a solution that works?