The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/claim-tariff-quotas-under-transitional-simplified-procedures?utm_source=11261705-c250-4a8b-bd10-d6018fd5380d&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate