How can I stand up for myself?

I’ve never been good at standing up for myself. I’m constantly talked down to and treated like a door mat. Like I’m just a stupid little girl who doesn’t understand anything. That I’m too dumb and naive. That I can’t say no. But no matter how often I tell myself I will prove them wrong I always cower and hide in my shell anyway.

Is there anyway to break this natural instinct? To stand up and show people I am worth while?

How can I stand up for myself?
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