The USSR was a communist country. A normal use of that term is that a country communist is one that's run by a communist party.

If you mean it didn't achieve communism, well duh communism is a hypothesized society achieved through socialism where the state ceases to exist. No socialists, including the people of the USSR, would think that their nation-state has achieved communism as that's oxymoronic. They would think of it as a transitional socialist state.