@Anonymous User
Double-check you have your new password correct by signing out on the tablet, and then signing in again, but enter all the details manually, don’t let the tablet put them in.
if this isn’t it, try your previous password on the TV.
if it works, then log out, and it should then accept the new one.
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.
