This is more important for test takers in Abbotsford.
For test takers in Vancouver, Surrey & Toronto, on the new registration system, your reference number is not that important, but it can be found in your IELTS account.
Abbotsford test takers:
Your Reference Number is emailed to you as soon as your submit your online application form in a message called IELTS Application Summary.
You will need your Reference Number to pay online and log into the Candidate Area.