You may have to wait for someone who has Now Broadband with Broadband Buddy to come along and explain it, as Now have not envisaged that anyone without Now Broadband might want to understand the process and help you here 😢
But go to:-
Click ‘Broadband Buddy settings’, change them, and give them 15 minutes to ‘take’.
If it doesn’t happen like it should, though, then please describe what does happen, with a screenshot if possible, so others can help you here.
Set a Payment PIN on your account so that no-one but you can buy memberships on it. Check your bank accounts monthly for any other unexpected payments to Now. That way you can at least nip them in the bud, while you and Now figure out whose fault they are.