There are several ways you can evade universal surveillance systems.
Live in places that actively destroy surveillance.
Cameras are valuable, and lots of people will actively loot and destroy them and sell them for parts, or deface them because they don't like being watched. Bad neighborhoods are always gonna be a thing. You can live in these places, and avoid doing any magic in outside locations where you might be watched.
They can also actively encourage the local humans to damage and destroy the infrastructure, forcing the elite to chose between chasing them and losing production.
Some areas of nature may be good hiding places as well. It's very expensive to have surveillance on an area where there are no repair crews nearby or electrical lines to tap into.
Live in the holes elites make.
The elites of the party aren't gonna tolerate being watched all the time, because then the watchers could destroy them when they indulge their drug use or perverted sexual habits or blood sports. They can work for the elite offering their services for protection.
Subvert the record keepers.
In any corrupt dystopia, every official is out for themselves. Heavy enough bribes will get you some degree of freedom and exemption from random checks.
Exploit factions within the leadership.
Some people want to chase them down and kill them, but the ministry of agriculture wants to grow crops. If the police kill a bunch of agricultural workers and they riot, heads will roll when they don't deliver enough food to the central government.
You can use that. Help ensure some regions are prosperous, so long as a blind eye is turned to your existence. Expose supernatural beings in your hunters, so that the hunters look corrupt. Make it as costly as possible to chase down the magic users so that other departments of the one world government argue that other priorities are more important.
In addition, offer your services to corrupt up and comers. If you can expose their rival as a demon (even if the rival isn't a demon) they may be willing to help you. A little telepathy to make them drink blood, and someone can get a promotion. A witch hunt is great for settling grudges.
Use subtle magic and find blind spots.
No system is perfect. Find the places where the monitoring isn't on, or make them with technology that interferes with cameras. Use subtler magic that can't be seen well.
Discredit the secret services.
The secret services are presumably sending teams of soldiers to kill or capture the demons. Work to exploit that. Have them accidentally kill a bunch of innocent children or women of the right ethnicity and put it in the media. Enough incidents like that and people will distrust the secret services and fear helping them and the government will be more reluctant to use them.
You can also work to exploit conspiracy theories. If a religious or ethnic community fears that the world government wants to exterminate them, they'll be much more reluctant to cooperate. Find the existing tension points and inflame them.
No system is perfect, deliberately so. There's always a way to break it.