@Anonymous User
Is it a 2017 Samsung TV? There are issues with these at the moment.
A NowTV Stick, £19.99 including a two-month Entertainment Pass worth £14.98, would tide you over until it’s fixed.
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.