AT&T Non-returned device charge

Phone in question is on an Unlimited plus post-paid plan with 5 lines.

After an AT&T NEXT every year upgrade, I made a mistake shipping my old phone back to AT&T and the device ended up arriving two days past the "return by date"

Prior to the "return by date" I called AT&T CS on the day I was re-shipping my old phone to notify them that it would now most likely arrive 2 days late; I was assured that this was okay and I was informed that my account was noted with the tracking number.

Fast forward to 11/28 I noticed that I had been charged for my old phone so I initiated an online chat with AT&T CS; the rep "confirmed" that my returned device fee would be credited back by my next bill and that my bill due date would be extended from 12/11 to 1/8/19 to allow time for the credit to be applied.

I left for a trip on 11/29 and returned home this morning 12/5 to find my that my phone was mailed back to me with a note stating that it could not be accepted because it arrived past the trade-in window. The phone was returned to me without prior notification, after being told my device would be accepted and having my "future credit" confirmed.

I was on the phone with AT&T CS for over 40 minutes this afternoon and the response I received from 3 different reps was that there was nothing they could do, the phone could not be traded in.

This is ABSOLUTELY PATHETIC customer service on behalf of AT&T to someone who has been a loyal customer since Cingular wireless, has 2 wireless accounts (one with 8 lines and one with 5), AT&T U-verse, and Directv. 

If the best AT&T can do is "discount" my bill by $10/month (basically putting the cost in line with the newer unlimited data plan) then I recommend anyone considering a switch to AT&T: stay with your current provider! Once you come over to AT&T, you're no longer a valued customer. You're just an account number with a monthly payment attached.