On that, friend, you are wrong. Unless you refer to the Zoroastrians and their mash-up of a theology, but I do not think they are 6,000 years old — maybe 4000. The ‘Satan’ as an independent godlike being which you seem to be demanding be recognized is a more recent invention.
That Satan is a the world’s greatest and longest excuse for misbehavior. But that’s all it is — an excuse.
To be clear, Satan certainly is a being, but certainly nothing like God.
I'm not demanding anything, as these are not MY ideas. The existence of Satan is clear and explicitly documented in Holy Scripture from Genesis to Revelation. He, in the New Testament, tempted Christ Himself on more than one occasion. That Satan exists is a foregone conclusion (not a debatable point of contention) of Catholicism, Protestantism, Judaism and even Islam.
The only way I'm "wrong" is if you're not a Christian, a religious Jew or even a Moslem.