raycast is returning object underneath another object

I'm trying to detect which game object the user has clicked, but the raycast is returning an object that is fully covered by another object. any clue how this is happening?

  //get where the user clicked the mouse in world coordinates.  Input.mousePosition returns a pixel coordinate
                 Vector2 worldPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);
                 RaycastHit2D hit = Physics2D.Raycast(worldPoint,Vector2.zero);
     
                 
                 if (hit.collider != null) {
                     Debug.Log ("confirm collision with " + hit.transform.gameObject.name);
                     switch (hit.transform.gameObject.name) {
                         // cancel X button pressed
                     case "confirmCancel":
                         Debug.Log ("this.gameobject= " + this.gameObject.name);
     
                         // get the upgrade script to enable the collion checking again
                         shopBg = (GameObject) GameObject.Instantiate(Resources.Load("shopBg"));
                         upgrade = shopBg.GetComponent<upgradeScript> ();
                         upgrade.confirmShown = false;
     
                         // remove this screen
                         GameObject.Destroy (this.gameObject);
     
                         break;