Boost as in Now Boost, or Boost as in TalkTalk Boost?
If the latter, you need to talk to TalkTalk, as you are paying through them.
Looking at the charges on your card or bank statement, what are the references given? NOW, or SKY, or what?
And if you asked your bank to stop these charges, and they didn’t, they owe you back every penny they paid out on them from the date you asked the bank to stop the charges.
But first, let’s find where they are coming from.
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.
If you take an offer that comes with a ‘free trial’ of Boost or another Membership, Cancel them straight away. You will still get the full duration of the trial, and if you decide you do want to continue with one or another of the trial products, just revisit the Cancel, and UnCancel it.