Custom character, problem with joints

Hello, I recently created my first custom character.

But I’ve run into some problems with my joints while I tried animating it, the torso, neck,lower toso and head movements were acting strangely, I have no idea what’s causing this, so I came to ask.

When I try to rotate the head, the hole body rotates.
If I try to rotate the torso, the rest of the body under the torso rotates.

Uploading: weapons - Roblox Studio 2021-08-30 21-54-32.mp4…

The limbs works fine

Alright so I fixed every part except for the neck/head

The head can’t be selected for animating
and the neck moves the hole body bellow, when I want it to only move the head…