The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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-nationals-living-in-the-eueea-and-switzerland-healthcare?utm_source=89ee6ec0-de4c-447a-adf4-319b0be0d7c6&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate