@Anonymous User
I thought TalkTalk had stopped doing Sky Boosts (assuming you are using Boost in the TalkTalk sense of the word).
So what do I know?
But I suggest you post your query on the TalkTalk Community, where they will likely be far more familiar with the ins and outs of TalkTalk TV vis-a-vis NowTV than here.
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.