The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/uk-students-in-the-eu-continuing-your-studies?utm_source=02cc0595-5bf6-4427-af34-84d632a543cd&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate