Issue with modems seen on the account

My daughter signed up for the internet service. She picked up the modem (XB7) yesterday afternoon from Xfinity office, Evanston, IL. However, she could not activate the service with that modem, we went back to the store again and they gave us a different modem to activate (XB8). We went back to the store in the afternoon to return the XB7 modem but the agent in the store could not give us the return receipt saying that he could see only 1 modem on the account (XB8). However, we can see 2 modems still on the account through the app, even though we had returned the XB7 modem. Can someone help me with removing the XB7 modem from the online account view which has already been returned so that there are no discrepancies later on.

Regards,

SG