Unreturned Equipment Charge

I have no idea why, but a $14/month "Unreturned Internet / " charge on my invoice. The note under it says, "Voice Equipment Is Inactive. To Avoid Future Charges, Please Return The Equipment To Your Nearest Service Center." Well, I have a Comcast provided voice modem that I pay $14 a month for, and it's definitely active! My data modem is my own and it's also fine.

I wish I could talk to someone in customer service, but the 800-Xfinity automated system won't let me speak to an agent. It pushes me to the "online assistant" and when I ask for help with an erroneous charge, it gives me the 800 number to call! Extremely frustrating. Not sure what else to do.