random number without repeating

hello, i created a method who choose a random number, but in some cases generate an infinite loop, i don't know why after repeating Random Range 6 times in the loop, the loop become infinit.

 public int initialSceneIndex = 6;
 public int lastSceneIndex = 15;
 public int[] scenesSelected = new int[] {6,7,8,9,10,11,12,13,14};

 public int GetRandomWorldSceneIndex()
 {
   
    int u = Random.Range(initialSceneIndex, lastSceneIndex + 1);
    int j = 0;
     
     for (int i = 0; i < scenesSelected.Length; i++) 
     {
         j++;
         if (j >= 30)
         {
             Debug.Log("infinite");
             break;
         }
       
         if (u != scenesSelected[i])
         {
            
             continue;
         }
         else
         {         
             u = Random.Range(initialSceneIndex, lastSceneIndex + 1);
             i = -1;
             Debug.Log("repeat");
             
             
         }
     }
     return u;
 }

i think in this case the answer always should be 15, the infinite loop only created when " Debug.Log("repeat")" is more than 6