1. 她从不在海水中游泳。 She never swims in the sea. 2. 我们从不违背自己的原则。 We never deviate from our principles. 3. 她从不知道为什么他们投反对票阻止她加入俱乐部。 She never knew why they blackballed her from the club.

You can say '我(过去)从不抽烟。'. So I think it should be 'I never smoked (in the past)'. 'I have never smoked' should be '我从未抽过烟。/我从来都没有抽过烟。'. They are different.

I never smoke. 从不 means never.

Maybe, I saw it in a dictionary example sentence translated as "will never".

It means "have never". In this sentence, 从 equals 从来. People often say that sentence when they are offered a cigarette. It implies "Thanks. I won't accept your cigarette. And the reason is nothing but I never smoke. "