What does it mean the serial number was for a product that was replaced

If it says the serial number was replaced* that likely means they were reported as defective and Apple replaced them but they were not returned to Apple as required, or they were reported lost or stolen from stock or during shipping. No support or service is available for them.

See my answer from last year. Somebody had the box and phone and reported them defective, but sold them to you instead of sending it back to Apple. It may not be defective at all, but in that case it is essentially stolen property.

I have the invoice and the box and phone and the three if them by the same serial number and i am the first user and i recive the mentioned message that the device is replaced how come?