Linked accounts

It sounds like you could be right, though I am not clear on how the link would be formed, or how to deal with this. Typically between exchanging a device you entirely erase the device so it is really factory new for the next user.

See if Apple can come up with a solution or explanation: Refer to this page for Apple Support features ➔ Contact - Official Apple Support

Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.

This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support

That happens when you are not using two account but a single one. Are you sure you are using two?