Enemy's NavMesh not working

Hey guys.

I'm new in Unity and I don't know why my code doesn't work. When range is under 15, enemy should chase player, but instead of this it stops. Also, it is a little lagged when arrives at each point. How can I resolve this?

 public Transform[] patrolPoints;
 public float moveSpeed;
 private int currentPoint;
 private GameObject Player1;
 private  GameObject currentPlayer;
 private bool Patrolling = true;
 private NavMeshAgent navComp;

 // Use this for initialization
 void Start () {        

     currentPoint = 0;
     Player1 = GameObject.FindGameObjectWithTag ("Player");
     currentPlayer = Player1;
     navComp = this.GetComponent<NavMeshAgent> ();
 //    transform.position = patrolPoints [0].position;
 }

 // Update is called once per frame
 void Update () {
     
     float range = Vector3.Distance (transform.position, currentPlayer.transform.position);
     transform.position = Vector3.MoveTowards (transform.position, patrolPoints [currentPoint].position, moveSpeed * Time.deltaTime);

     if (Patrolling) {

         if (transform.position == patrolPoints [currentPoint].position) {
             currentPoint++;
         }

         if (currentPoint >= patrolPoints.Length) {
             currentPoint = 0;
         }

         if (range <= 15) {
             Patrolling = false;
         }
         //transform.LookAt (patrolPoints [currentPoint].transform.position);        

     }

     else if (Patrolling == false) {

         //transform.position = Vector3.MoveTowards (transform.position, currentPlayer.transform.position, moveSpeed * Time.deltaTime);
         navComp.SetDestination(currentPlayer.transform.position);

         if (range >= 20) {
             Patrolling = true;
         }
     
         }

     }
 
 }