Why do I have to give notice to cancel even though my contract has ended?

My 24 month contract ended 5 months ago. I am trying desperately to cancel my service and move on, the internet service was absolutely horrible the entire 2 years, and we paid 3 times more for it than local competitors charge, so we're done. I called to cancel and was told we had to give 30 days notice to do so and was sent a docusign asking me to agree to pay for another 30 days for this service that I am no longer using, since we switched companies. Customer service told me that unless I agree to pay for another 30 days, they will keep billing me and will not shut off my service and close the account. I looked at my original contract and it says " Customer must provide thirty (30) days’ prior notice to Comcast in order to terminate a Service Order or the Agreement. Any termination of a Service Order or the Agreement may be subject to early termination fees in accordance with the Business Services Customer Terms and Conditions." But this service order contract that I signed was for 24 months and has since expired. The contract has already terminated. So why do I still need to give notice if that contract and everything on it that I originally agreed to, has ended? I have contacted my state AG and the FCC about this. I am not in a contract, I am not using the service, I should not be forced to buy my way out! How is this not extortion?