First line of Capital by Karl Marx : "The wealth of those societies in which the capitalist mode of production prevails, presents itself as “an immense accumulation of commodities""
Average life of worker under capitalism - Work, make wages, buy stuff with wages, repeat.
Average life of worker under USSR - Work, make wages, buy stuff with wages, repeat.
It is this condition of the working class that communists seek to abolish. The working class in USSR suffered the same impersonal domination of the value-form as working classes everywhere.
The USSR could not be communist because communism is an international movement, not something that can be realized in a single nation. Look at any capitalist country, trade(exports and imports) makes up a giant chunk of the GDP.
The USSR called itself communist because since the Stalinist counterrevolution, they were simply opportunists who seek to enforce their own different version of capitalism while pretending they were communists (ring a bell? China, Cuba, NK all do the same thing)
Communism is the real movement of the working class to abolish their present conditions of existence, and replace it with one where there is no longer any domination of capital over man, nor is there domination of man over capital, but capital literally doesn't exist anymore.
There is no money, exchange, wage labor, commodity production, profit and other such categories in a communist society.
Such a society can only be achieved by an international movement of a revolutionary working class led by a class party that follows the principles of scientific socialism(aka Marxism).
Hope this is clear. If you want to understand more, read the following texts
"Communist Manifesto" by Marx, "German Ideology" by Marx. And these following ICP party texts.
https://www.marxists.org/archive/bordiga/works/1958/marxism-property.htm
https://www.marxists.org/archive/bordiga/works/1957/fundamentals.htm https://www.marxists.org/archive/bordiga/works/1926/lyons-theses.htm. If you spend the time and effort to understand these 5 texts, (it will take 6 hours at most) you will already be a better communist than 99% of self described communists out there, online and IRL, who simply do not understand the basic concepts of what communism is and what actually has to be done.
Actual communists are few are far between in leftoid spaces