gameobject.transform.position not working correctly,

hey guys, I try to move the player back to the center of the map after each round of combat,but it didn't work ,here's the code:

      if (!GameObject.FindGameObjectWithTag("Player"))
             Instantiate(player, new Vector3(-mapSize.x / 2 + 0.5f + mapCenter.x, 0.5f, -mapSize.y / 2 + 0.5f + mapCenter.y), Quaternion.identity);
      else
         {
             Debug.Log("111");
             //player.SetActive(false);
             player.transform.position= new Vector3(-mapSize.x / 2 + 0.5f + mapCenter.x, 0.5f, -mapSize.y / 2 + 0.5f + mapCenter.y);
             //player.SetActive(true);
         }

It is so weird! I already try setActive(false) but no available, hope anyone can help.