We have not seen god. It does not mean that god does not exist
We've not seen Unicorns and Elves either, does that mean they exist?
Everything imaginary exists within the imagination because it is recognizable in terms of other, known forms.
So unicorns, for example, are only imaginable because horses exist and because horned animals exist. If they didn't, then the concept of a unicorn would be unthinkable.
God is the ultimate composite identity. He is the unification of all powers and aspects of the universe, known and unknown.
Can we say that things exist that we don't know about? Yes, we know from experience that there are always unknown things beyond the horizon of our current awareness/understanding.
Nothing exists except insofar as it was created from some pre-occuring form or state. The law of conservation of energy/matter is that energy/matter cannot be created or destroyed; so it always transforms from an earlier state.
If the universe is thus in a perpetual state of creation without beginning or end, we can attribute that to a creator beyond time and space. That is possible because it is possible for us to conceive of creation without beginning/end, thus we have to account for the universe's capacity to be aware of itself and understand itself beyond its own infinite nature.
Big bang theory works like this. People ask, "what came before the big bang?" but the notion that time and space can be traced backward without reaching some absolute limit beyond which nothing earlier could have occurred implies that space/time have always been expanding but yet we are capable of analytically conceptualizing the notion of the universe expanding from a single point origin.
Whether the big bang theory is correct or some other theory, the fact that we are conscious and capable of contemplating the universe's origins/history by observing how things work and extrapolating prior causation implies that the universe contains latent potential for knowing itself and being aware of doing so, hence the capacity to describe ultimate creation in terms of an ultimate creator.
Whether or not you can stand to make the leap from thinking in terms of 'creation' to identifying it in terms of an ultimate creative agent, you have to acknowledge that the human mind is capable of taking all the complexity of a living organism and identifying it in terms of centralized agency.
It is this same capacity to identify individuality in a collection of interworking parts that also makes it possible for us to identify individuality at the level of the entire universe of creation.