Hi Day,
Having supplied you four names of ancient Greek philsophers who may be reasonably interpreted as not believing in god / gods, I see you merely repeat your assertion without any citations.
->DB> One point that they all agreed on was that God existed.
Kathleen Freeman translated all known fragments of the Presocratic philosophers that were collected in Diels' authoritative collection _Fragmente der Vorsokratiker_ (5th ed., Berlin, 1934,5) in her book, _Ancilla to the Presocratic Philosphers_, London, Oxford, 1948.
Protagoras was born in the latter half of the fifth century B.C., and according to her, wrote the books, On Being, and On the Gods; from the latter book, the following quotation survives:
"About the gods, I am not able to know whether they exist or do not exist, nor what they are like in form; for the factors preventing knowledge are many: the obscurity of the subject, and the shortness of human life." (fragment 4, at page 126, Freeman).
It is a reasonable inference that this, at minimum, agnostic approach, would extend to any "God" --single or supreme deity-- although you have not defined this term for the Greek context.
Hal.