If you want to watch movies, you need Cinema;
if you want to watch TV programmes, you need Entertainment;
If you want any of;
to watch in Full HD;
to have 5.1 surround sound instead of stereo;;
to watch On Demand programmes without adverts;
to watch on up to three devices at once, rather than just one;
then you need Boost.
Work out what you do and don’t want, and cancel any of the three memberships you don’t need.
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.