Unfortunately,on most ISP services,the "tail"(that is the personal number of your ISp varies each time you log on.
An ISP Number consists of three sections
The main number (The ISP providers number)
The local area ISP number(in my case the area near Rye,East Sussex)
Then (the important bit) your personal ISP number,which as I say can vary from log on to log on.
So even if AB blocked the whole number,due to the fact that the "tail" of the number changed it would be a bit pointless,.
I am a moderator of another forum, and I and the other mods went into this in depth with a BT Broadband Technical Helpdesk,and the above was what I was told.
Only if AB can moderate all the categories more throughly can we weed out such posters,but that seems unlikely.
Given also the ease with which one can register on Ab with another username,by using an very easily obtained free Hotmail account,this would aslo seem to defeat any such moves.
I appreciate how annoying it is,but these people revel in the aggro they cause,one of the best ways to defeat them is to ignore them.
Not easy but effective,starve them of attention and they die.