"The Universe was spawned at some point. Therefore some body of mass must have existed before the creation of the universe, that is the make up of what is now the universe. We know this is true because of the given that matter can neither be created nor destroyed. So in order for the universe to exist as it is now, some reaction must have taken place to get the result of the universe. However there can be no reaction if there is no action to begin with.
THEREFORE THE UNIVERSE DOES NOT EXIST.
Or, if you prefer, the universe does exist, and the original first cause must be that some deity triggered the reaction that resulted in what is now the universe."
Or the law of causation does not apply to the origin of the universe, because the law of causation requires time to preceed the event in order that it can work.
The beginning of time is literally an event without a cause, because time did not exist before the event.
It is the law of causation that that causes the contradiction, so it is the law of causation that is not necessarily true.
The law of causation is a rule we have made because every event we have ever observed, we also observe a cause. So we assume it is always true and turn it into a universal law.
All laws are assumptions based on a repeated observation holding true. The assumption is that they apply everywhere in the universe and every time throughout the universe despite the fact that we have not checked them everywhere. But it is extremely reasonable to assume that because other places in the universe do not differ too much, the laws apply there too.
But applying laws to places or times that are very different to the one we observe the laws holding may not be reasonable.
It's like observing that every mark on a long tape measure has a mark preceeding it. So we make the rule "every marked inch on the tape measure has a marked inch before it" and if we stick to around the middle area of the tape measure, it will hold true for every point we test. But as soon as we test the beginning of that tape measure, we find that the rule no longer works there. An exception which should have been considered seeing as the beginning of the tape measure is a unique place.