What are the reasons you don't believe this theory?

[Zenith]

Let's say I come and say:

There are 12 gods that created the universe with the earth as it is and with all its beings, along with us. They have afterwards gone to another world, through a portal. Now one of them returned and told me the truth and told me to tell everyone that there are actually 12 gods and many other things about how things really are. I tell you these things, and they have logic, do not contradict modern science, etc. And then I tell you that if you don't believe what I've told you, then you will be punished by the gods after death.

I'm sure that none of you would believe me. So the question is: what are the reasons you don't?

I know a few reasons, but I am curios about your opinions.