sorry to hear that you’ve had this issue too.
Unfortunately, those completing these investigations have a very rigid view that no mistakes can be made at point of dispatch. If your invoice says iPhone 15 Pro Max, they will say that it’s not possible for any other device to have been dispatched. So it must have been switched by either the courier or yourself. The courier will complete an investigation and confirm that nobody tampered with the parcel.
They will also ignore any request to check this thread.
Even after I spoke to an exec, they agreed to replace my device (which has arrived), but for security purposes couldn’t disclose whether anything had gone wrong and how. They wouldn’t accept responsibility. It was like they were doing me a favour, giving me a phone that I’d paid for.
Was it a brand new, legit iPhone SE? Factory sealed etc? You can check the serial number here: Check Your Service and Support Coverage - Apple Support