Unexisting blocks colliding and existing block not colliding

Hey, so I'm creating a bad copy of minecraft that I won't release and I'm having problems with collisions, for some reasons I sometimes with unexisting blocks and I don't collide with existing blocks, anyone that can help me with it?

Movement code (and collision code too)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Player : MonoBehaviour
 {
     public bool isGrounded;
     public bool isSprinting;
 
     public Transform camera;
     public World world;
 
     public float walkSpeed = 3f;
     public float sprintSpeed = 6f;
     public float jumpForce = 5f;
     public float gravity = -9.8f;
 
     public float playerWidth = 0.15f;
     public float playerHeight = 1.8f;
 
     private float horizontal;
     private float vertical;
     private float mouseHorizontal;
     private float mouseVertical;
     private float verticalMomentum;
     private bool jumpRequest;
     private Vector3 velocity;
 
     private void FixedUpdate()
     {
         CalculateVelocity();
         if (jumpRequest)
             Jump();
 
         transform.Rotate(Vector3.up * mouseHorizontal);
         camera.Rotate(Vector3.right * -mouseVertical);
         transform.Translate(velocity, Space.World);
     }
 
     private void Update()
     {
         GetPlayerInputs();
     }
 
     void Jump()
     {
         verticalMomentum = jumpForce;
         isGrounded = false;
         jumpRequest = false;
     }
 
     private void CalculateVelocity()
     {
         if (verticalMomentum > gravity)
             verticalMomentum += Time.fixedDeltaTime * gravity;
 
         if (isSprinting)
             velocity = ((transform.forward * vertical) + (transform.right * horizontal)) * Time.fixedDeltaTime * sprintSpeed;
         else
             velocity = ((transform.forward * vertical) + (transform.right * horizontal)) * Time.fixedDeltaTime * walkSpeed;
 
         velocity += Vector3.up * verticalMomentum * Time.fixedDeltaTime;
 
         if ((velocity.z > 0 && front) || (velocity.z < 0 && back))
             velocity.z = 0;
         if ((velocity.x > 0 && right) || (velocity.x < 0 && left))
             velocity.x = 0;
 
         if (velocity.y < 0)
             velocity.y = checkDownSpeed(velocity.y);
         else if (velocity.y > 0)
             velocity.y = checkUpSpeed(velocity.y);
     }
 
     private void GetPlayerInputs()
     {
         horizontal = Input.GetAxis("Horizontal");
         vertical = Input.GetAxis("Vertical");
         mouseHorizontal = Input.GetAxis("MouseX");
         mouseVertical = Input.GetAxis("MouseY");
 
         if (Input.GetButtonDown("Sprint"))
             isSprinting = true;
         if (Input.GetButtonUp("Sprint"))
             isSprinting = false;
 
         if (isGrounded && Input.GetButtonDown("Jump"))
             jumpRequest = true;
     }
 
     private float checkDownSpeed(float downSpeed)
     {
         if
         (
             (world.CheckForVoxel(transform.position.x - playerWidth, transform.position.y + downSpeed, transform.position.z - playerWidth) && (!left && !back)) ||
             (world.CheckForVoxel(transform.position.x + playerWidth, transform.position.y + downSpeed, transform.position.z - playerWidth) && (!right && !back)) ||
             (world.CheckForVoxel(transform.position.x + playerWidth, transform.position.y + downSpeed, transform.position.z + playerWidth) && (!right && !front)) ||
             (world.CheckForVoxel(transform.position.x - playerWidth, transform.position.y + downSpeed, transform.position.z + playerWidth) && (!left && !front))
         )
         {
             isGrounded = true;
             return 0;
         }
         else
         {
             isGrounded = false;
             return downSpeed;
         }
     }
 
     private float checkUpSpeed(float upSpeed)
     {
         if
         (
             (world.CheckForVoxel(transform.position.x - playerWidth, transform.position.y + playerHeight + upSpeed, transform.position.z - playerWidth) && (!left && !back)) ||
             (world.CheckForVoxel(transform.position.x + playerWidth, transform.position.y + playerHeight + upSpeed, transform.position.z - playerWidth) && (!right && !back)) ||
             (world.CheckForVoxel(transform.position.x + playerWidth, transform.position.y + playerHeight + upSpeed, transform.position.z + playerWidth) && (!right && !front)) ||
             (world.CheckForVoxel(transform.position.x - playerWidth, transform.position.y + playerHeight + upSpeed, transform.position.z + playerWidth) && (!left && !front))
         )
         {
             verticalMomentum = 0;
             return 0;
         }
         else
         {
             return upSpeed;
         }
     }
 
     public bool front
     {
         get
         {
             if
             (
                 world.CheckForVoxel(transform.position.x, transform.position.y, transform.position.z + playerWidth) ||
                 world.CheckForVoxel(transform.position.x, transform.position.y + 1f, transform.position.z + playerWidth)
             )
                 return true;
             else
                 return false;
         }
     }
 
     public bool back
     {
         get
         {
             if
             (
                 world.CheckForVoxel(transform.position.x, transform.position.y, transform.position.z - playerWidth) ||
                 world.CheckForVoxel(transform.position.x, transform.position.y + 1f, transform.position.z - playerWidth)
             )
                 return true;
             else
                 return false;
         }
     }
 
     public bool left
     {
         get
         {
             if
             (
                 world.CheckForVoxel(transform.position.x - playerWidth, transform.position.y, transform.position.z) ||
                 world.CheckForVoxel(transform.position.x - playerWidth, transform.position.y + 1f, transform.position.z)
             )
                 return true;
             else
                 return false;
         }
     }
 
     public bool right
     {
         get
         {
             if
             (
                 world.CheckForVoxel(transform.position.x + playerWidth, transform.position.y, transform.position.z) ||
                 world.CheckForVoxel(transform.position.x + playerWidth, transform.position.y + 1f, transform.position.z)
             )
                 return true;
             else
                 return false;
         }
     }
 }