There isnt an additional cost, if I offer the service it just allows me to see the screen your facing.
If you would like to reset your security questions this can only be done on the phone, where they can ask you billing information etc.
You can contact Sky on 03300 412 546, unfortunately there is a rather long wait time currently.
When prompted enter in your phone number,
Then state your looking to "change my password",
When asked if your calling about username and passwords, say "yes"
You will then be asked if your call relates to the yahoo security breach say "no"
A member of the account team will answer your call and talk you through how you can change your security questions.