Flex box is not free

2 years ago when I was renewing my Xfinity customer service in the phone asked me if I wanted a flex box and said it’s free. I said no I don’t need it but they sent it anyway and said it’s free and doesn’t need to be returned. Now I just canceled my service and they said I need to return the flex box and I have no clue where it is since I never tried to set it up.