The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/eu-domain-names-what-you-need-to-do-to-get-ready-for-brexit?utm_source=aa2c4f98-f5a8-4667-b166-725df2d5f45c&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate