Random UPS bill recieved?

Today I got bill from UPS, it states There was a difference between the true weight it was marked as "20pnds" was truely 34.8pnds. Thus wanting me to pay a $15.05 difference. But here is the thing! The sender information IS correct, minus the zipcode which is a zipcode 20 minutes from my location. After reviewing the invoice, I noticed the receiver name wasnt listed in any of my receipts, neither was the Tracking number it gave. So I called them, and the first guy to pick up said it was a incorrect delivery and it was supposed to be delivered to apartment "13" but got delivered to "11" instead, WAIT HOLD UP! I havent shipped to ANY apartments! and scary enough its in the same state. The "pickup" date is listed as 4/29, my newest receipt is from 4/21. and its to Chicago, not florida. Every UPS package has been a EBAY Transaction, so i went to see if someone had complained about not getting an item, but nope... every single item was marked delivered, and every buyer had listed positive feedback. The Heaviest thing i had sold was a Monsterpower Powercenter, and that was not even CLOSE to 35 pounds...also I've shipped my things from the exact same UPS Store EVERY TIME, How can there be a weight difference if they weigh it before they say how much it will be to ship! so i explained everything shoddily to the guy on the phone and got transferred.. After I got transferred, i was told the department I needed was closed for the night so I have to wait, but How should I go about this.... I cannot pay this fee, not for a mistake on UPS's behalf.