Make sure that your trans map is pure white and black, not coloured. Black for invisible, white for visible, grey in between. (Kind of basic, sorry if you already know this.) The map must be plugged into the Transparency node - the name of the node doesn't matter. The Transparency value must be set to 1.0, the Transparency_Edge also to 1.0, and make the Transparency_Falloff 0.0 - this should give best results. If this doesn't help, please post a screenshot of your material room settings, and a render of how it's coming out.

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"you are terrifying
and strange and beautiful
something not everyone knows how to love." - Warsan Shire