Whats my Account number?

Your account number is available in the "Manage plan" page

My Plans -> Manage Plan below your phone number you have Account ID

or

check on your service agreement

https://fizz.ca/en/faq/how-can-i-view-my-service-agreement

How to find your Services agreement:

1- Go to My Plans in your Fizz account.
2- If you have multiple plans on your account, you will see them all here.
3- Click on Manage plan for the plan you wish to view.
4- In the Manage interface, scroll to the bottom and select Services agreements.
5- All your Services agreements will be listed here by date. The most recent Services agreement document is the one that applies to your current plan.

Or in the transaction history
https://fizz.ca/en/transaction-history

To see a list of all your Fizz transactions:
1- Go to My Plans in your Fizz account.
2- If you have more than one plan, choose the plan you wish to see transactions for.
3- Scroll to the bottom of the usage summary and click on Transaction history.