I found Jay Earley's book "Self-Therapy" very helpful in getting to know/defuse/befriend my own hostile inner voices. It basically teaches you a self-guided meditation (you have a sequence of questions to follow) where you meet with each voice/part-of-you as it comes up, and get to know what it's trying to do for you. The overall stance is that each voice however poisonous started out trying to (ineptly) protect some other part of you, probably back when you were a child and saw the world in pretty simplistic terms.
If for example you had a teacher that shamed you when you made an error, a part might have taken on the responsibility of preemptively copying that teacher's belittling voice, in order to "help" you not have to face that shame in real life anymore. Twenty years later it's still using that not-so-bright strategy, and you don't even know why you're so hard on yourself when you don't do things perfectly.
You get to know the voice and talk with it as though it were its own independent personality. Once you do that, you can learn about and talk with the "victim" part too, then the protector part that's been dogging you for years can finally relax from its role and ultimately take on a more constructive role in your life.
Voice by voice you build internal allies out of the voices that used to torment you. The cool thing is that after a while I started looking forward to other voices coming up because now I know how to work with them.
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The book that introduced it to me is Self-Therapy: A Step-By-Step Guide to Creating Wholeness and Healing Your Inner Child Using IFS, A New, Cutting-Edge Psychotherapy
by Jay Earley.
Then Internal Family Systems Therapy
by Richard C. Schwartz (which was actually written first) covers the same process from a different angle, focusing more on how two voices can be "polarized" against each other and refuse to change until the other one changes first. It's a factor that comes up pretty commonly but Self-Therapy
doesn't cover much. I read both books back-to-back.
I've found them very helpful. You might check out the sample chapter on Amazon to see if it resonates with you.