Whats the deal comcast? Saying I still have a set-top box when I got confirmation they were complete

I got rid of tv services a few days ago, I sent in a return for 3 boxes, all of which were completed today. Now they have a new device on my account x1 top box with a different serial number and an new option to return it. What in the heck is going on here? I'm not paying for that, I sent back all the equipment that was given to me. If you messed up by replacing the top box and didn't cancel the old topbox out before you installed the new one, thats your bad not mine. I returned all my devices.

What are they trying to pull here? I can't even get ahold of anyone right now.