You mention that the SM asked you to back date your votes. The SM did this in writing or verbally? If the former, then you’re on solid ground.
In my experience a SM is little more than the post box for or microphone of the OC. Before applying to NCAT against the OC you will need to apply for mediation with the OC (which they may or may not attend). It will take no less than 6 weeks from when you apply online for mediation until the matter is heard.
Be sure of what you want to get out of mediation.
If mediation fails, only then you can apply to NCAT. That’ll be heard no less than 8 weeks after you apply for it. As I mentioned earlier, complain separately about the SM and hopefully you, like me, will get a positive outcome against the agent which will fortify your case at NCAT.
Best of luck.