You should have

1)Raised a hue and cry right there
2)Gathered a couple of witnesses and complained to FPSC authorities. Since this was a FPSC hall, there office is also in the same complex
3)These halls also have CCTV footage which could have provided evidence along with eyewitness accounts

In the end, the harsh reality is that making threads here won't do any good to your cause. Everyone already knows this and frankly I wouldn't tell you what else happens. The account you narrated is nothing and represents the 'pettiest' of what can be done and what is being done.

In short, next time you see something like this, take action