I don't "presume" the existence of God. That's a shallow strawman. Why can't you argue against the actual position.
To use the word
presumption flies in the face of overwhelmingly vast human experience of and evidence for theism.
...if [God] doesn't need a cause why does the universe.
God doesn't need a cause. He is a personal being not a planet or a galaxy or an asteroid.
If you think planets and galaxies etc don't need a prior cause you're free to hold that belief.
...If you're going to argue that everything has a cause and then presume that not everything has a cause I really don't see how the subject can be intelligently discussed.
I don't argue that everything has a cause. God doesn't have a prior cause.
And I assume you don't claim everything has a cause either.
So where is the disagreement?
Yep. No argument there. Now...
Can you prove it
caused itself to come into existence?
Can you prove it spontaneously (mysteriously) came into existence by pure chance?
Can you prove it has
always existed forever and ever? Science says it's only 13.7 B. years old.
No, of course you can't and I don't expect you to either - unless you assert that such scenarios are MORE plausible than a Big Bang which was deliberately caused.
Maybe God the great Astro-Physicist has a divine Hadron Colider and He caused something to be created out of nothing. Lawrence Krauss would be impressed.