Recovering parents' student finance accounts

Hello,
My older sister set up my parents' student finance accounts when she went off to university, but she no longer has their details (e.g. secret answer, passwords). I can't recover their accounts because my sister linked their accounts to a phone number and email address that she has lost.
I spoke to student finance on the telephone and she said I should update my parents' details by post because it doesn't match the ones on the system (which is not up to date). So I can't recover their accounts because of security. She told me that it'll take 40 working days, and I was wondering if updating the details online would be faster?
If this is possible, is there any evidence I need to include with the letter?
I feel a bit lost on what to do because I'm stuck in the application process and can't move on to provide my parents' financial information since I can't access their accounts.
Any help would be greatly appreciated, Thank you!

Hi Kajn,
Were you advised to have your parents complete a PFF2 form instead, or was this never mentioned?
Thanks, Graeme

Hi Kajn,
It takes around 14 working days for the letter to be processed so that they can access their accounts. If they have failed the authentication, it is best they do this. In the meantime however, they can still support your application by completing the below PFF2 form which you can upload to your account for review. Our current processing timescales are approximately 6 working days with subject to change depending on our current volumes.
https://media.slc.co.uk/sfe/2526/ft/sfe_pff2_form_2526_o.pdf
Thanks, Clare