To me, it feels like in English this particular phrasing would usually be followed by a statement that clarifies or adds further context to the first part of the sentence, for example: 'I never have used pink soap, but I might use it in the future'
'I never have used pink soap, and I don't intend to start using it now'
'I never have used pink soap, but I am fond of the blue variety'
That's... difficult. "Nie używałem" would be my first thought - I never used to use pink soap, I just never used something like that.
"Nie użyłem"... sounds as if there was some specific bar of soap and you're telling someone: "I assure you, this bar of soap hasn't been touched, I have never used it!" - so basically, someone assumes that you did. That's at least my impression.