If scientist have made small particles of matter then why do we still haw the law of conservation of matter? Is it because the few particles don't make a noticeable difference in our life?
For one thing, you're probably thinking of the law of conservation of mass. Calling it "conservation of matter" is technically inaccurate because matter isn't a quantitative property of a physical system, and only such properties have conservation laws.
Now with that detail out of the way: there isn't really a law of conservation of mass, either. But you can have an effective law of mass conservation, if you can safely ignore any processes that convert particles with one mass to particles of a different mass. In daily life, we can always do that, because the kinds of processes that involve particles of different masses just don't occur under normal (for us) conditions. But if you're dealing with high-energy particles, there are lots of processes where the masses of the inputs and outputs differ. That's how we can create bits of matter, by taking advantage of those processes.