Why do the police never respond to me?
They should be. If you are consistently getting no reply, get a screenshot of all of the officers online at the time and head to teamspeak (ts.straya.life, find the command lobby) and let them know that you aren't getting responses on your dispatches, alternatively use a complaint form (can be found in the Police teamspeak descriptions).
If you need assistance e.g your car has broken down, call EMS instead, they might be able to help. Alternatively for your best bet in getting a response back, find the highest ranking police officer online (See next question) and directly message them.
How do I know what officers are what ranks in game?
Every officer has a callsign, with their callsign indicating their ranks, they are as follows (I will be referring to the first letter in the callsign, starting with highest going to lowest). The letter at the end of their callsign in game dictates which station they are a part of e.g S, Sydney, B, Brisbane, M, Melbourne)
F - Commissioners/Cabinet
C - Chief Superintendent
B - Superintendent
T - Inspector
S (Numbers lesser than 10) - Senior Sergeant
S (Numbers greater than 10) Sergeant
K - Senior Constable
O - Constable
Z - Probationary Constable