How do I mute other people during conversations?

Hey, my problem is quite simple. I often have necessity to talk with unpleasant folks. Most of them don't show any politeness, they interupt my every sentence. Is there an app that allows me to mute "theirs side" of call, for me to be heard by them and not another way around? Turning down my call bar speaker to minimum (it doesn't go below 25%) still makes them loud.

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