The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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.playfootball.net/enquiry?day=saturday&product_category_url=join-a-league&product_id=350&product_type=league&venue=mottingham-coldharbour&hide_choices=true&utm_source=email&utm_medium=FA&utm_campaign=coldharbour_FA_flyer_U16_U19