Withering away of the state: https://en.wikipedia.org/wiki/Withering_away_of_the_state

Yes. "A communist state" is an oxymoron. Communism is by definition stateless. Government/governance, sure, but without a state. Rojava would probably be a better example of communism (in practice) than Soviet.

"state" is area where government is able to collect taxes and respected by other governments. Thus "communist state" is not oxymoron.

I don't understand your point.

> A communist society would entail the absence of private property and social classes, and ultimately money and the state (or nation state).[1]

[1] https://en.wikipedia.org/wiki/Communism

I was born in communist country. No money, only objective points to describe cost of production and egibility, no police but militia, one "united" workers party and tax in nature and goods. But no money ;D and no state ;D