I returned the comast rental model in 2017 May, and thought the Comcast will remove the charge. But then I found out that Comcast kept charging me a year latter after I have returned the modem. I wasn't paying attention to the bill as I setup auto payment and paperless statement.
I called the customer service today asking for the credit back, but was told that the maximum they can credit me back is three-month overcharge.
Now I cancelled the autopayment and switched the paper statement. I saw a lot of threads that other comcast clients got charged in the same way (http://forums.xfinity.com/t5/Customer-Service-Archive/Repeatedly-billed-for-returned-modem/td-p/2949...).
It's hard to believe Comcast making money in this way. I wish I never have set up AUTO PAYMENT.
I can help research your equipment charges. Can you please verify your first and last name, full street address, and the phone number or account number associated with your services in a private message?
To send a private message click on my name "ComcastChe", then click private message me.