Cant remove old cable box from my bill

Going back to somewhere around 2015 my son lived with us. At some point he wanted to upgrade, which I was not aware of. Once I found-out I said 'No !'
As a result, you, the cable company were expecting to receive the cable box to complete the upgrade, which never arrived. Therefore, you added the cable box to our bill. 
Once I contacted you and explained all of this, you said once I actually do an upgrade and hand the box in that will come off of the bill automatically.
A few years ago I did do an upgrade. I have a new cable box and a new router. In fact, I went to the Xfinity Store locally so I can hand - in the old box. 
Here I am today now, I still have this old box on my cable bill. I have tried two times through chat to get it fixed - each assured me it was taken care of. 
However, I look at my balance today and it is still showing a balance reflecting that old cable box portion of my bill. 
I want that removed from our bill - plain and simple !!
Like I said, recently I have tried the online live chat two times to get this fixed -- still not removed !!