What @gavs82008 says. Now actually sent me a voucher for an Amazon Firestick to use instead when discontinuing Now on my 2015 Samsung JS9000.
And I have another Firestick keeping the flame of Now alive (see what I did there? 😛) on a 2012 32” Samsung TV we have, on which nearly every smart app has dies, even the BBC iPlayer.
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.