Service cancelled but bill keeps coming - Why are you screwing a customer of over 3 years?

This is the sorry of someone who has fulfilled a three year contract with Comcast Business and paid my monthly bill every month for internet and phone service for these three years.  I continued with your service after the contract expired until recently when you upped my bill from $134 to about $324.  Can anyone say outrageous?  OK so I informed you I would be cancelling and switching to Xfinity for internet and phone.  Comcast Business service was terminated on Sept. 29 when Xfinity showed-up and activated their service.  As everyone knows Xfinity is owned by Comcast.  A few moments ago I called Comcast Business to ask why I was sent another bill for the time period Oct. 7 to Nov. 6, they explained about some small print on the form which they make you sign in order to terminate the service.  So basically Comcast Business is trying to screw me out of another $324 for service they are no longer providing me.  If this is not a crime, it should be and you should be ashamed of yourselves.  I switched to another branch of your own company and you are still trying to screw me out of over $300 even though I've paid you over $4,000 over the last couple of years.  This kind of crap is why people hate big corporations.