Newgistics return taking forever

Hello,

I have returned my device using label I received from AT&T customer service and it is stuck for almost 3weeks now in a USPS location. Due to this i'm being charged for monthly installment payments without the device in use and neither am I eligible to upgrade my device to a different one. I have been in touch with AT&T multiple times and they are being helpless. All I got is a case has been received, once AT&T receives the device, they will remove installments from my line which is never happening. I suspect the device is lost in transit, Usually it should take only 3-5days for the return to be delivered, now it's 20+days and it is still in the same origin location where I sent from.