I believe I should add that this may not be enough, because after communicating with the narcissist, the "voice" may not only be in accusatory attacks etc. The narcissist may still be there for you afterwards in a variety of everyday activities in which you have allowed him or her to be.
It can be a certain area of activity, art, etc., in which you have disclosed too much to him, and which your mind associates with the narcissist as an interlocutor on that subject.

Thus, often when you meet some object, or do an action, or thoughts themselves come to such a subject, which for the mind is associated with the narcissist, there can be an uncontrolled imaginary reference, a conversation with the "introject" of the narcissist. Psychology uses this term to refer to an imaginary, unreal persona based on external perception of somebody.

Why are we discussing this topic on an esoteric website? Esotericists (at least I do ) have an opinion that narcissists are driven by entities. At the same time I also believe that introjects are, in fact, entities. There are various occult texts about man's ability to create entities by the power of imagination, etc. Certain "introjects", I believe, are precisely the entities that control the narcissist himself, i.e. the person has not, in that case, created them. It is a "demon", as they say, that rules over a narcissist and also tries to disturb a person.

It must be said that introjects have a special energy. What is it? The thing is that it is your energy. You have to understand that in reality the person that you thought the narcissist was, does not exist and never has existed. The narcissist is a non-personality, it is a something, a hole, an empty space, something non-personal, a blackness with a mechanism of adjusting and putting out different masks: attractive, frightening, copying some aspect of you, etc., towards psychopathy - a mask completely copying you in all aspects. Thus, you perceived a mask and formed an imaginary "person" out of your own energy, so it's dear for you, and thus has had some stability, you've been upholding it.
Despite the possible physical separation, the cessation of communication with the narcissist, people often continue to "have a word or two" with their imaginary something.

Your task: end these uncontrollable episodes of "communication" with the introject. How can you do this? Briefly: Control your thoughts when you "enter" a topic in which you and your narcissist have had something in common. Move forward in that topic without communicating that imaginary "something", thus depriving it of a feeding of energy. Step forward and keep this-newness, the energy of newness-to yourself.