What did Persians call Mesopotamia?

it is nimrod becuase after the chaldeans came to power there they called it nimrod as well.

I don't know about earlier and later eras, but in the third century A.D., when Shapur I was fighting to recover northern Mesopotamia from the Romans, he called it "Asuristan" (Assyrian country).

In the Achaemenid Period, there was no single Persian word for Mesopotamia, at least in the beginning.  Northern Mesopotamia was called Athura, "Assyria" and southern Mesopotamia was called Babirush, "Babylonia".  In 482 BC, Babylon revolted from king Xerxes.  At the end of the revolt, Babylonia lost its status as a satrapy and was incorporated into Assyria.  Mesopotamia became administratively, the satrapy of Assyria, for some years thereafter.  By 448, we read of a restored satrapy of Babylonia. 

At least in the earliest years of the Sassanid Period, we know of Persian shahrs of Mesan (Babylonia), Asoristan (southern Assyria), and Nodsiragan (Adiabene, or northern Assyria).