At&t's shipping company lost my return phone

I returned two phones, my original and my DOA 1st replacement device on the 20th of June 20, 2018.  Both phones were shipped separately using the return shipping labels provided.  I started receiving phones calls about my returns shortly after the ten day mark on the first return.  I provided the tracking info and thought the issue was resolved.  I kept receiving calls from AT&T and I even went to the post office to see why there wasn't any tracking info generated.  The post office told me that both packages were picked up by AT&T's shipping company the day after I dropped them off.  I am still receiving phone calls and emails reminding me to return my devices even though I supplied my tracking info and showed proof of there shipping company having picked up both phones.  The nightmare that followed no customer should gave to experience.  I was on the phone literally over 7 plus hours trying to resolve this issue without a resolution.  I was given the phone run around and pass off several times, I was transferred to the incorrect department multiple times and had to wait as long as 30 minutes on hold.  I was transferred to the wrong department multiple times and I had several calls dropped when the agent said they were transfering me and were going to wait on the line.  AT&T's service and customer care have deteriorated over the past couple of years. I have proof both phones were returned and I am still on the hook for them, I am told to wait longer yet it has been over 30 days since both phones were sent back.  Eventually they were able to locate one of my phones and told me they received it on the 26 of June, six days after shipping it.  Where is my other phone AT&T?