I know some of the heretic sects of ancient Christianism. Some of them didn't believe that God created the Universe, and some others didn't believe in the Trinity. I was wondering if a branch of Christianity that didn't believe that Jesus Christ was the real son of God ever existed.
Yes. The Ebionites were an early branch of Christianity that taught that Jesus was the Messiah, but rejected his divinity. They were based primarily in Syria, and never grew to be a large sect. By about 400 ad they apparently no longer existed. Most of what we know about them comes from polemics accusing them of being judaising heretics, so much of what we know about them is debatable and is inferred from negative writings about them. Many modern scholars believe that their beliefs were similar to those of most early Christians; but again, this is debatable.
Can you clarify, do you mean a) didn't believe that Jesus was the Son of God, or b) didn't believe that Jesus ever existed, or c) some combination of a & b. Your question involves a run-on predication and it's unclear which you mean.