Its most likely a $10 modem rental fee. Call them and explain you dont have rental equipment. Or visit a store and tell them, so they can repay you for the fee they keep charging and remove it permanently.
No need to call in. I can help by starting an equipment research ticket for you that will investigate this. In order assist you, please send me a private message verifying your first and last name, street address including city state and zip code, and the full account number or phone number associated with your services.
To send a private message click on my name "ComcastChe", then click private message me. If I don't reply right away, I will reach out when I get back in the office. My working hours are Sunday-Thursday's 2:30-11 PM MST.