The contradiction lies with your take on determinism.
Yet you can't point out any such contradiction...
You claim that all our choices are determined by past events, but our conscious awareness has no control over past events because it exists in the present. It defines our present. For conscious awareness to have any input on choices, it must be free from the past in order to do so, otherwise it is just a spectator over what has already been determined.
Firstly this is just an
appeal to consequences fallacy. You do get that you not liking a conclusions doesn't mean that it's wrong, yes?
It is also nonsense. The program in a chess computer isn't a spectator, it is what is actually making the choices. The mind of a non-human animal isn't a spectator, it is what is determining its behaviour. In both cases (for very different reasons) the behaviour is being determined in real time - no part of the systems can sensibly be described as spectators.
No matter how many times you repeat it, talk of "the present" in this context is meaningless twaddle. Our consciousness is exists in time. Thoughts enter it, get mulled over, choices get made, and we move on to something else.
Here, yet again, is the real contradiction: if every thought that enters your consciousness and every conscious choice you make is not entirely determined by its antecedents (all the possible things that could influence it), then part of the reason for it must be unrelated to its antecedents and must therefore be random.
It is not convoluted, it is simple and straightforward. Neither is it based on material or physical assumptions. I emphasised consciousness because that's what you seem obsessed with but the logic is completely unrelated to consciousness because it applies to any system at all the develops its state over time - as human minds in particular, and any choice making system at all more generally, quite obviously do.
And I'm still waiting for any hint of the logic you said you had, or the honesty to admit you have none.