There may be good reasons why the recommendation was not acted upon. If the IG cannot find concrete proof, he cannot resolve the case in your favor. Just because you say your supervisor violated the rules does not make it a proven fact. It is human nature to tend to look at things from a very personal point of view. Some people assume that the commander has intervened and muzzled the IG if they do not hear the results of the investigation immediately.
Heavy workloads require time.
Do not assume that a negative answer from the IG is wrong just because it doesn't suit you. If you are absolutely certain the answer is wrong, and if your have some additional evidence to support that certainty, the case may be reconsidered. If, on the other hand, you are merely unhappy because the report does not go in your favor, it is pointless to continue presenting the IG with the same complaint and the same evidence. You will also save yourself and others a lot of time and avoid unnecessary frustration.