Hey @Chi4 and thanks for reachin gout.
Your final bill will be sent to your billing address following your next billnig cycle.
From there, you won't need to calculate anything.. The amount will be directly showing up on your last invoice.
Also, if your account is totally cancelled, you can still have access to your online account to see the PDF version of your bill.
You will need to make sure that your username is your Email address.
If not, you can simply register as a new customer on Fido.ca for MY ACCOUNT.
Hope this helps.