Hi Clare,
Thank you for reaching out to us in our community and welcome, I am sorry to hear you haven't been able to set up a online account due to your account number only being 8 digits long.
I have tried to have a look at things our end however was unable to find your account with the details we have for you, the issue you are having is a easy fix and I am sorry this wasn't advised, when the account number is under 9 digits you just put the missing amount of digit in with 0's.
Kind regards
Paul.