Being charged for a full month of services after cancellation

I disconnected my DVR equipement in August.  I wasn't able to get around to contacting customer service until the beginning of September to cancel my services.  The website told me I had to schedule a call, and the earliest call I could get was September 10th more than a week later (this is already ridiculous).  I talked to someone on the 10th, and she said she would cancel my service and try to put in a request to back date my cancellation, as I haven't used the service in 5 years.  I couldn't cancel sooner because I couldn't get to the equipment to disconnect it.  She also said to go ahead and remove my credit card from auto pay so that I wouldn't get charged.  It's fine that back dating it didn't work, but considering I tried at the beginning of September to get my service cancelled, I don't believe I should be paying for September.  Instead I'm being charged for almost the entire month of September.  Please help.  There were already plenty of years of paying for service I wasn't using, please don't charge me for a month after trying to get my service cancelled.  It's obvious Xfinity doesn't make it easy to cancel for this purpose (I should've just been able to fill out a form online to begin with)