ICSTIS doesn't have the power to ban anyone from accessing the UK telephone network. The network is owned by BT, and that's a privately owned company, so if anyone is to do any banning it would be BT.
Think about how difficult it would be to operate such a ban - you ban 'Naughty dialers inc.' on Monday, and on Tuesday they pop up again as 'very naughty dialers inc. You would be banning companies so fast you wouldn't have time for anything else. The key to this is to arrive at a situation whereby BT doesn't pass funds to premium number holders quite so rapidly - allowing time for people to dispute their bill and het an investigation going. The problem is that BT is in business to sell Telecoms services, and holding onto customers' money for a couple of months isn't the best business-building strategy in the world.