The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/accounting-for-import-vat?utm_source=44b8917b-4abc-41a5-bb05-5e89d992048b&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate