Your CO is quite likely not to reply to an email which just asks for an update. They are under extreme time pressure, working around 100 cases at the same time in rotation. If they were to send regular updates to EVERY one, which would be only fair if they did it for ANY one, that would take out about one working day per week, and, not surprisingly, INZ wants them doing work that progresses cases instead.
This is why, if you just have that urge to say, 'I am still here waiting - tell me something,' it is to the INZ call line that you can do it and get told, 'It is with the CO being processed,' or similar.
If and when the CO has anything to tell you, or needs more information, you can be sure that s/he will get in touch with you.