Mobile Device Return

I have made multiple attempts to set up a return of a mobile smartphone.  The device was not activated, the service cancelled and it remains in an unopened box, never used.  The Xfinity agent advise me that I could take the phone to a local Xfinity store to process the return but they were not able to process a return.  I attempted to set up an online return but no option to return the device is available via that route.  Please advise the process for return this phone as I do not need it and do not want to continue to pay to purchase it.