How are you trying to play them, from the browser, or direct in the App?
Normally, I would advise you to try another browser or to delete and reinstall the app, but I worry that this might result in your downloads being deleted 😢
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.