A mosquito can bite you. But if it doesn't bite hard enough or in just the right spot, you won't notice... even if you feel it a little. But if it bites you just a little harder, you will slap at it. It prompted you to act. If it hadn't prompted you, you wouldn't have acted. No free will there. simple a set pattern.
No matter what you think or do, how do you know that there isn't something prompting you to do it? Maybe there are many little things that jointly push you to think or act in a specific way. Since you can't put your finger on any of them, you think that you had free will to choose what you chose.
Starving kids in Africa can choose to eat all they want. But they can't eat if there isn't any food. Does the fact that they didn't eat prove that they chose not to eat? So, why would the fact that we get some of the results of our choices be the determining factor that we had free will?