Like Whizz said, you will find unsubscribe info here https://fizz.ca/en/faq/unsubscribe.
To be sure you don't receive unexpected charges, you can also remove your credit card info from your account.
This is teh frustrating part, if you have no service and your account isn't active you can't cancel. The only way to cancel is to unsubscribe from your account page. If you don't see the option on your account to unsubscribe, then you are stuck until your account is active.
If you can't get help from support then you will have to contact the CCTS like I did and someone there will ensure you refund you for your costs and help you to resolve the issue if Fizz fails to be able to unsubscribe your account.
Go to this page https://fizz.ca/en/faq/resolving-issues, and make sure you are logged in. Wait 15 seconds for the bubble icon to appear at the bottom right of the browser and click on the icon to chat with support. Try a different browser if you have issues getting the bubble to appear.
You can also send a message via facebook messenger
https://facebook.com/fizzca and click send a message
You can also fill a contact form from you account webpage.
Once logged in, from the account panel go to My Profile -> Contact Form and fill out the form and someone wil email you back us
If you still can't get help you would have to file a complaint with the CCTS to persue a resolution.