“从来不” is an adverbial phrase meaning 'never (throughout the past up to now)'. It emphasizes that an action or state has not occurred even once from the speaker's perspective up to the present. You must use it with a negative verb phrase — it already contains 不, so you do not add another 不 or 没. The structure is: 从来不 + Verb. It is stronger and more emphatic than 从不 or 从不曾. Common in spoken and written Chinese.