“Or the Universe has existed always...”
Nope, no luck with that approach if you are trying to be rational. It’s been proven to be mathematically impossible to have an eternal universe that is also expanding, as we have observed this universe to be:
Of course the universe doesn’t need to be eternally expanding.
And the rules by which it expands can change as scales change, just as quantum mechanics is different from macro mechanics, making any ‘proof’ that posits similar rules at differnt scales rather irrelevant.