The correct spelling of the phrase "not let went" is actually "not let go." The word "went" is incorrect as it is the past tense of "go," while "let go" is a phrasal verb meaning to release or relinquish control. The correct pronunciation of "let go" is /lɛt ɡoʊ/, with the stress on the first syllable of "let" and the second syllable of "go." It is important to pay attention to correct spelling and pronunciation to ensure effective communication.