Isn't Communism just extreme oligarchy.

One is an economic system the other is a political system.

Tomato tomato. The point is both are centralized, unlike textbook capitalism and the free-market economy.

If your logic ignores that A and B are different then you literally claim anything and thus it is pointless to dialog with you.

No, you are mistaking that for Stalinism. Communism would not have a hierarchy that allows for oligarchy. Read Marx or Kropotkin.