Return of equipment

I returned all the equipment that was hooked up.  I am a 67 year old professional retired engineer.  I do not steal or keep equipment. I packed it all up 3 pieces and cords and took it too the local UPS office.  When I dropped it off the UPS office said one piece was not on the list, I said this is everything that was hooked up.  This is it.  Please send it all back.  He said ok.  Now i get a letter saying I did not return one piece of equipment.  I am NOT a thief nor do I have any use of this equipment.  How or where do I go to tell someone my problem?