How to cut people off?

I’ve been friends with these girls for a long time. It’s like they don’t like me but they’re constantly trying to be in my space. Sometimes I mistake kt for friendship but I know better. I don’t know how to cut them off. I don’t talk to anyone at school. But I want desperately to be away from them. They belittle me and just talk down on me. I hate it but I don’t know how to do it. Sometimes I think I’m overreacting. But like how do you just cut off someone who has spent years trying to dim your light? I don't know it should be easy but in a way it worked bad I don’t know how to cut people off. I feel restricted. They always make me feel bad about myself. But what’s the first step?
How to cut people off?
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