service cancellation

I already cancelled my service for August 6th, which was last week. I received an email confirmation, although it was missing the date. My account doesn't show anything about a cancellation and today I received a new bill for the next month. I already have new people living in my house. Xfinity Assistant wants to schedule a callback for Friday while today is Monday. there is no way to do this online, or even write or call. None of the other services I cancelled were this difficult. What can I do to finally get this cancelled?