It seems that your shame comes from blame, sweetie. You blame yourself for how you've been treated. Internalised that so much that your mind uses the feeling to try and protect you from harm.
"It's my fault I'm treated this way"
"If I didn't feel so wrong in my own skin, none of this would be happening"
"I shouldn't say anything or do anything about it because then no one can hurt me"
Sound familiar?
That seems at the root of all this, hon. Your shame is an emotional manifestation of the flight response. The urge to run. To go somewhere safe, if ultimately painful in a different way. Your mind sees it as the lesser of two evils. Better the devil you know, as it were.
To get past it, you have to look for ways to absolve yourself of the blame. Something that may well be quite exceptionally hard to do, with it being deep-rooted from childhood. And me telling you that you don't have anything to blame yourself for in all of this won't stop you feeling the shame. It's something you have to be able to tell yourself... and believe it.
Maybe a start is to look for some positives in your life. Little things. Things that make you feel confident as you are now. Instances where you're treated how you want to be treated, you know? Accepted and free to live the way you want to live. Write them down, see how they make you feel. And then think about what's different between those experiences, those people, and the people you knew as a kid. Think about how much both you, and the kind of people you've interacted with have matured, and don't have that infant mindset anymore.
It may be a gradual thing, hon, but you CAN get past this. One step at a time. You have a legitimate problem that you're rectifying more and more every day. You're actually being yourself. Asserting yourself. That can be scary sometimes, for sure. But it's a testament to the strength you have inside yourself that you're still here, and you still know what you need to do. Whatever the world has thrown at you, it hasn't broken you. That speaks volumes.
If people around you bring you down, and cause you pain... rather than hiding yourself from them out of shame and fear... try to remember that the power is in your hands. The power to assert yourself, or to remove these people from your life and surround yourself with more positive people, ones who see you and accept you for who you are. You've done it before, sweetie. Remember how that made you feel. THAT is the feeling when there is no blame. Strive for that.