The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/government/publications/leaving-the-eu-advice-for-eu-businesses?utm_source=b994e217-bef2-4661-b53c-94427b6a5f2e&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate