Why would one not start by using the main 'reporting' line on 08456 007 010? That is the reporting centre and they would be able to transfer you to the centre itself if it warranted it.
I imagine they don't go doling out the number willy-nilly.
cassa, I had to speak to the fraud dept about 6 months ago, if i remember correctly i rang Th telephone banking number and explained what had happened and they transferred me through to the fraud dept.
I can only surmise that maybe Cassa doesn't like talking on the telephone (which I can relate to) so particularly wanted to send them an e mail instead, though having said that, if it was something quite urgent like reporting fraud I'd take the quickest route on hand. Hope you managed to get it sorted anyway Cassa.