How to solve problem involving RigidBody.Constrains

Well, i need to freeze my X rotation, Y rotation and Z position after i've created my gameobject. But for some reason only the last constraint i wrote (the z position) gets freezed, even if i've told my script to freeze all three of them. Here's my code.

 public List<GameObject> Mobs = new List<GameObject>();
     public GameObject Mob;
     
     // Use this for initialization
     void Start () 
     {
         Mob = GameObject.CreatePrimitive(PrimitiveType.Cube);
         Mob.transform.localScale = new Vector3(1f, 1f, 1f);
         Mob.AddComponent<Rigidbody>();
         Mob.rigidbody.constraints = RigidbodyConstraints.FreezeRotationX;
         Mob.rigidbody.constraints = RigidbodyConstraints.FreezeRotationY;
         Mob.rigidbody.constraints = RigidbodyConstraints.FreezePositionZ;
         Mob.AddComponent<Mob>();
         Mobs.Add(Instantiate(Mob, this.transform.position, Quaternion.identity) as GameObject);
     }

Any ideas? Thanks for reading.