I am serious, call local TV station. Get the investigative reporter to dig on it. Bet you in a heartbeat UPS will "fix" it all. They will leave you alone forever. The LAST thing they need going into the Christmas season is bad press and make people second guess using UPS, then they will use UPSP, DHL or FedEx.
My dad worked for a TV station for 40+ years. You would be AMAZED at the power of bad press.....
Newspapers too. Heck, get that guy on ABC News 20/20 "Give me a break" John Stossel to do it, they would LOVE one like that. National coverage? UPS will be knocking at your door with apologies!
EDIT: Please PM me with details, I will try to get a hold of a guy who used to go to my church who was high up in UPS, like a VP, if he is still there and I can find him, then maybe I can have him look at it. Give them an internal opportunity to make it right and leave you alone. Tell the Collection Agency it isn't your bill and that they are not allowed to contact you again with this bill. Tell them to send it back to UPS.