The views expressed in this post are my own personal (HRA protected) views, and are not representative of any organisation I have any involvement with.
I had a reply within 2 days from the ICB, then another to say they were still looking into a question I had. I have then had another saying they were now actioning it. It has taken a month so far, but they have kept me up to date with what's going on, so my own experience has been OK.
Have a look in the spam/ junk folder. I had some of my emails end up there, or so I was told when I chased up an answer to a query I had emailed (that was some time ago now)