Get in Touch (all the options, including leading you to the Broadband Support number you would perhaps do better to call rather than using Live Chat):-
https://help.nowtv.com/gb/get-in-touch/
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.
