What's the solution if they continued to monthly charge me after trial version cancellation in September?
Sorry to hear that you are facing trouble. Unfortunately, you won't find the help you need at these forums. These are peer-to-peer forums, with no one here having access to your account information. You need to contact support.
To contact support see the instructions given at the link below
Also, be mindful of answering anyone who sends you a private message. See the following for more information about scammers
You should have received a confirmation email when you cancelled. Check your spam folder.