What can i do to have a flat stomach?

I tried a lot of things in order to have a flat belly.For examples,diet pills, diet tea,cleanser, exercising,and Other more. Furthermore I just done with my sixth treatments of vela-shape,unfortunately I don’t see result. Even thought I ‘ve recently lost 20 pounds by dieting and exercising but my belly still looks big. I’m desperate I don’t know what else to do.Can someone please tell me what can I do ?