If you can assert that the world is determinant, therefore free will doesn't exist then it is just as valid for me to assert that free will exists, therefore the world is not determinant.
That would be libertarianism. From wiki: libertarianism is an incompatibilist position which argues that
free will is logically incompatible with a deterministic universe. Libertarianism states that since agents have free will, determinism must be false and vice versa.
There is also compatibilism, which says that determinism is true but is compatible with free will. That's obviously not your position. You are a libertarian. Now the discussion is about free will. Here's a logical argument:
The world is determinate, free will is not compatible with determinism, therefore there is no free will.
Two premises and a conclusion.
Your argument is:
There is free will, free will is...
Whoa, hang on. Back the truck up. You've used the conclusion as a premise. You can't do that otherwise you will get a circular argument. It's actually a good example of begging the question, when an argument's premises assume the truth of the conclusion. Which is what you are doing.
There is free will, free will is not compatible with determinism, therefore there is no determinism, therefore...there is no free will.
That doesn't work. You can't use the premise 'there is free will' to get to a conclusion that 'there is free will'. So we'll go back to mine. If you want to reject the argument, you have to reject the premises or claim that the conclusion is logically invalid. NOT just that you disagree with it. If the premises are correct then the conclusion will be as well. And you have a complaint about the first premise. Prove it! you say. So I say that all effects have a cause. If you want to refute that then all you have to do is give an example of an effect that doesn't have a cause.
I'll give you another example so you can see what you have to do:
All swans are black, you are not allowed to kill a black swan, therefore you can't kill any swan.
You have a complaint about the first premise. And all you have to do to disprove it is show me a white swan. If you can't but believe there are some, then the best you can do is get me to change my argument:
On the assumption that all swans are black etc...
That premise will hold until you produce a white one. So...on the assumption that the world is determinate...then that premise will also hold until you show me otherwise. And the conclusion will hold. And if you claim it's not then it will be ridiculously easy for you to show me. But with which you seem to be having an enormous amount of difficulty...