How do i unclog kitchen sink?

I've used a small electric sewer machine, and a 50 ft sewer machine and my kitchen sink still wont unclog. I used chemical to unclog down drain, and it didnt work. So then I used the sewer machines and it is still clogged up. I am using sewer machine it in the drain that goes down into ground behind kitchen sink. What else can I do. They rest of the house is fine no plumbing problems just my kitchen.