Please see https://www.xfinity.com/support/internet/cancel-my-xfinity-services/. Unless an employee responds to your message here, it's best to contact one of their reps at the phone number on your bill or 1-800-Comcast, or visit a Service Center (check locations and hours at http://www.xfinity.com/support/service-center-locations/).
If possible, get written confirmation that your account was closed, as they sometimes "forget". Also, if you have any Comcast equipment to turn in be sure to get a receipt for it and keep that receipt forever. See http://forums.xfinity.com/t5/Billing/How-to-View-Pay-your-bill-Online-and-or-Secure-your-Account/m-p.... Comcast is in the habit of "forgetting" that equipment has been turned in and billing you for it months or years later.
Hi nabuzarifah, If you are still needing assistance I can help cancel your account. Please send me a private message with your account information (Name on account, address on account and account number).