Function is being called even when not told to

I'll get to the chase, basically I have a box around my character, and whenever that box touches an enemy it adds to a list if it hasn't been added already. This is so that I can attack multiple enemies at once, and it works great.

But here's my problem, as soon as I kill an enemy only SOMETIMES does Unity throw and argument exception about the list being out of range from the index I'm using.

And I know exactly what's causing it, my enemy is dying before I even call the attacking function; which is strange because I haven't even called the function yet to make it take damage and potentially leading to death.

Here's my code:

Firstly, I go through a loop for all enemies that are in the list:

 if (canAttack && Enemies.Count > 0) {
 
                     for (int i = 0; i < Enemies.Count; i++) {
                         if (Enemies [i] != null) {
                             print ("enemy i is not null name is " + Enemies[i].name);
                             StartCoroutine (WaitForAttack (i, Enemies[i].transform));
                         } else {
                             print ("enemy i is null");
                         }
                     }
 
                 }

Next, I call the "WaitForAttack" coroutine that way the damage is "lined" (lack of better word) up with my attacking animation.

     IEnumerator WaitForAttack(int i, Transform IT)
     {
         print ("i name " + Enemies [i].name);
         yield return new WaitForSeconds (attackTime);
         if (Enemies.Contains (IT) == false) {
             print ("null " + IT.name);
 
         } if(Enemies.Contains(IT) == true) {
             //Enemy is dying before we call the attack function
             Attack (Random.Range (minDamage, maxDamage), Enemies [i]);
         }
     }

Unity also oddly enough still claims it has the enemy in the list, as you can see I'm checking. Also, it only happens after the WaitForSeconds() function.

Lastly, the attack function:

 public void Attack(int dmg, Transform obj)
     {
         if (called == false) {
             called = true;
 
             shaker.ScreenShake ();
 
             GameObject b = (GameObject)Instantiate (blood, obj.position, Quaternion.Euler (0, 0, Random.Range (-360, 360)));
 
             Vector3 s1 = new Vector3 (1f, 1f, 1f);
             Vector3 s3 = new Vector3 (1.5f, 1.5f, 1f);
 
             int r = Random.Range (1, 3);
 
             if (r == 1) {
                 b.transform.localScale = s1;
             }
             if (r == 2) {
                 b.transform.localScale = s3;
             }
 
             print ("Attack");
 
             GameObject t = (GameObject)Instantiate (attackText, obj.FindChild ("hitTextPos").position, Quaternion.identity);
             t.transform.FindChild ("hitText").GetComponent<Text> ().text = dmg.ToString ();
             Destroy (t, 2);
 
             EnemyHealth hp = obj.GetComponent <EnemyHealth> ();
 
             hp.Hurt (dmg);
 
             called = false;
         }
     }

You might tell me that it's something wrong with my WaitForSeconds() function, and you could be right, although as I've said this happens about 75% of the time, other times it executes the way it's intended to and doesn't throw up any errors.

Sorry if I'm a bit vague; I'm tired and frustrated. Ask any questions if you need to!