Stopping a rigidbody immediately

I'm very new to Unity and C#. I have a cube rigidbody that I am trying to stop once I release a movement key(WASD, etc). However, when I release the key the cube slides just a bit and that is what I am trying to prevent. I have maxed mass, velocity, material physics, and all in between with no success.

 private Rigidbody rb;
 private float moveHorizontal;
 private float moveVertical;

 public float maxSpeed = 10;

 // Use this for initialization
 void Start () {

     rb = GetComponent<Rigidbody>();
     moveHorizontal = 0f;
     moveVertical = 0f;
 }
 
 // Update is called once per frame
 void FixedUpdate () {

     moveHorizontal = Input.GetAxis("Horizontal") * -maxSpeed;
     moveVertical = Input.GetAxis("Vertical") * -maxSpeed;
     rb.AddForce(moveHorizontal, 0, moveVertical, ForceMode.VelocityChange);

     //Limit Speed
     if (rb.velocity.magnitude > maxSpeed)
     {
         rb.velocity = rb.velocity.normalized * maxSpeed;
     }

    //Stop Movement
     if (Input.GetAxis("Horizontal") == 0f && Input.GetAxis("Vertical") == 0f)
     {
         rb.velocity = Vector3.zero;
         rb.angularVelocity = Vector3.zero;
     }
 }