I am sorry to hear about this. You can remove the add-on via My StarHub App (MSA) under your TV subscription add-on, or via My Account Manager (MAM) at https://secure.starhub.com/myaccountmgr/#/. You will be informed of any charges incurred (If any), before you remove the add-on.
To prevent accidental purchases, do be advised to set a purchase PIN. More information can be found at https://www.starhub.com/personal/for-your-home/tv/fibre-tv/parental-control.html?icid=int-31B-StarHu...
Hope this helps.