Another Jump Question

Hi Guys

I m having trouble setting my groundCheck flag to false the change state is there but my character is still able to jump to infinity.

I have assigned groundCheck to my ground prefab. which is on my ground layer. i have also assigned the mask to the ground layer. what am i missing?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class playerController : MonoBehaviour {
 
     bool isGrounded = false;
     public float force; 
     public float maxSpeed;
     public Vector2 jumpHeight;
     public Transform groundCheck;
     public LayerMask groundLayer;
 
     private Rigidbody2D rb2d;
 
     void Start () {
         
         rb2d = GetComponent<Rigidbody2D>();
         }
         
     // Update is called once per frame
     void LateUpdate () {
         float moveHorizontal = Input.GetAxis ("Horizontal");
         float moveVertical = 0;
 
         isGrounded = Physics2D.OverlapCircle(groundCheck.position, 0.001f, groundLayer);
 
         if (rb2d.velocity.magnitude < maxSpeed) {
             Vector2 movement = new Vector2 (moveHorizontal, moveVertical);
             rb2d.AddForce (movement * force);
         }
 
 
             if (Input.GetKeyDown (KeyCode.Space) && isGrounded) {
             isGrounded = false;
             rb2d.AddForce (jumpHeight, ForceMode2D.Impulse);
         }
         
         
     }
     
 }