> Potentially unrelated, but isn’t anarchy-communism also an oxymoron?

Communism implies anarchism.

> How could you enforce communism under anarchy?

Communism, as a state, is the hypothetical self-sustaining stateless end-state envisioned by Communism, the ideology. Socialism (an intermediate state in the theory), and State Capitalism (an intermediate state—and one most real regimes claiming Communist ideology get stuck in—in practice) may need enforcement, Communism, almost by definition, does not (whether it os attainable is, of course, a different question.)