I must confess-I thought carr barring only barred 'premium rate' numbers such as 0906 etc, as opposed to mobiles.
I didn't think you could bar mobile numbers?
It looks like (from what you have described) your friend rung up & asked for call barring (thinking it covered mobile calls), ntl enabled it, but as it only barrs premium numbers the bill was climbing due to mobile calls being made, but I'm not sure how ntl are to blame if they switched on the service that your friend asked for??
If they told him that the bar
would apply to mobile calls of course, then that's a totally different matter.