Get a copy of the original bill from the city. Call WCB and ask if they paid it. Basically you just need to do some work to find out what happened in the first place.
They may have sent it out and it was lost in the mail. They should have record as to where the first bill was sent which is why you need to get the original. If it was sent to the wrong address it doesn't mean you don't owe the funds but you could then say you wont pay the interest.
Reality is once it hits the statute limit they can't pursue legally as long as you don't acknowledge thedebt in writing or make any type of payment (this resets the limitation period).
http://credit-collections.ca/statute-of-limitations-on-canada-debts/