Charging Me for a Device I returned with Smart Label

ATT,

I don't understand why I am being charged for a non return of phone. I upgraded my phone, received the new phone, sent and returned the old phone with your smart label and am being charged $254 because you can't find it.

Your label shows it was picked up by the agent and I can't walk it into Washington DC where it was shipped.  I have been on the phone for hours trying to fix this.  Between being sent offshore and in the States this is an unfair use of my time.  I have 6 devices and am at my breaking point as I don't need this.

I am being told by a CSA that because it is not showing movement it is on me.  How is it one when it shows I did my part?  I brought it to usps and they scanned my return so how am I responsible?