Could you please try to challenge your beliefs. Just think, "what if I'm wrong?" "What if the doctor is telling the truth?" Can you not see how unlikely it is that what you think is true? The police laugh because what you say is so far feched not because they are involved in anything.
Can you try to distract yourself from thinking about gang stalking? Start a new course or find a new hobby?
I don't know you but I am distressed by how distressed you are over this. Nobody should have to go through what you go through. But the truth is that it is your mind playing tricks on you. And you've believed it for so long it's going to be difficult to challenge it. I hope that you can get better. But you need to see that you have an illness. Unless you realize you have an illness you can never get better.