Nothing to be done but to continue having patience. What you describe is absolutely normal.
The CO's job is to verify every single piece of evidence you have submitted, often by checking with third parties, some of whom may feel no urgency about replying. The CO also has to consider if what you have said about yourself fits with every detail of the regulations.
While all that is going on, the CO is ALSO working about 100 other cases in rotation with yours. S/He takes the first file, reads any replies that have come in, ticks off anything that can now be ticked off, and sends out any further queries that have arisen, then puts that file to the back, takes the next case and does the same - and so on, and so on. Whatever replies come in go to the relevant file, wherever it is in the CO's rotating queue. The CO won't see and deal with those replies until that file has once again worked its way to the front of the queue for its next turn for his/her attention. So you see, your mental picture of a CO who ought to be dealing with your affairs the moment you have replied to him/her is very wide of the mark.
Your application is in the hands of a government bureaucracy, dealing with tens of thousands of applications at the same time. There is a system, and you're in it. The end WILL come, but timing is not predictable. Meanwhile, for the sake of your peace of mind, try not to concentrate on INZ - think about other, ordinary life stuff, instead.