Delete EdgeCollider issue

In this program, When i draw a hill, a car can road on it's surface, and when I draw another one, the previous hill should remove.

but unfortunately the previous edge collider looks still there. this is what i've done for delete this collider :

        if(col)
        {
            col.Reset();
            col = null;
            Destroy(col); 
        }

unfortunately nothing works :) col.enabled = false is also doesn't work

this is the code: i don't know what i have to do to disable the previous collision

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class LineFreeDraw : MonoBehaviour
{
    private LineRenderer line;
    private EdgeCollider2D col;
    private bool isMousePressed;
    private List<Vector2> pointsList;
    private Vector2[] pointsArray;
    private Vector3 mousePos;

    // Structure for line points
    struct myLine
    {
        public Vector3 StartPoint;
        public Vector3 EndPoint;
    };
    //  ----------------------------------- 
    void Awake()
    {
        // Create line renderer component and set its property
        line = new GameObject("Line").AddComponent<LineRenderer>();
        line.material = new Material(Shader.Find("Particles/Additive"));
        line.SetVertexCount(0);
        line.SetWidth(0.9f, 0.9f);
        line.SetColors(Color.green, Color.green);
        line.useWorldSpace = true;
        isMousePressed = false;
        pointsList = new List<Vector2>();
    }
    //  ----------------------------------- 
    void Update()
    {
        // If mouse button down, remove old line and set its color to green
        if (Input.GetMouseButtonDown(0))
        {
            if(col)
            {
                col.Reset();
                col = null;
                Destroy(col); 
            }

            isMousePressed = true;
            line.SetVertexCount(0);
            pointsList.RemoveRange(0, pointsList.Count);
            line.SetColors(Color.green, Color.green);
        }
        else if (Input.GetMouseButtonUp(0))
        {
            isMousePressed = false;
        }
        // Drawing line when mouse is moving(presses)
        if (isMousePressed)
        {
            mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            mousePos.z = 0;
            if (!pointsList.Contains(mousePos))
            {
                pointsList.Add(new Vector2(mousePos.x, mousePos.y));

                line.SetVertexCount(pointsList.Count);
                line.SetPosition(pointsList.Count - 1, (Vector3)pointsList[pointsList.Count - 1]);

                CarIsCollide();
            }
        }
    }

    private void CarIsCollide()
    {        

        col = new GameObject("Collider").AddComponent<EdgeCollider2D>();



        // Collider is added as child object of line
        col.transform.parent = line.transform;

        if (pointsList.Count < 2)
            return;


        pointsArray = new Vector2[] { pointsList[pointsList.Count - 2], pointsList[pointsList.Count - 1] };
            col.points = pointsArray;

    }

}