The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.
https://www.gov.uk/guidance/studying-in-the-european-union-after-brexit?utm_source=d8ed3c46-6270-4eb9-bab1-84a5bf222862&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate