Lenin called a transitional phase that was intended to take 6 months to establish and another 6 months to phase out into socialism “state capitalism” (it may be the case that “war communism" of 1918-1921 was officially recognized as something of an extension of that phase necessitated by emergency), but state capitalism was never officially the long-term policy or the self-description of the state of the economy past that point; the criticism from non-Leninist Marxists is that what the steady state of what the USSR became was state capitalism, not socialism.
(Did he really say just 6 months?? That doesn't sound right. But anyway it would have only been a prediction -- which failed.)
"Joseph Stalin abandoned the NEP in 1928 with the Great Break."
That's not what wikipedia says. I can't argue as I am no expert in such matters myself having read almost none of the primary material (but I did read "The Tax In Kind"... which I was assuming outlined the theory of the NEP).
Wikipedia on NEP:
Lenin considered the NEP as a strategic retreat from socialism. He believed it was capitalism, but justified it by insisting that it was a different type of capitalism, "state capitalism", the last stage of capitalism before socialism evolved.[15]
_Lenin_ called it "state capitalism." That was the official policy of the USSR under Lenin. State capitalism.