Old modem equipment I do not have

Last year I was at an Xfinity store and they noted it looked like I had several old Gateway modem/boxes that I would be charge for at some point.  I believed we returned them all but made a search and there are no old prior devices just the one I have now.  I've been in this house >20 years and know where everything is and all prior devices have been returned as is required when replacing.  I would like to have any old devices (I do not see evidence on this on my bills but as noted this is what I was told) so there is no "ghost" equipment associated with my account.  Thank you