PHP - Fatal error: Uncaught Error: Call to undefined function

I know this is a widely asked question, but I cannot, for the love of me find the answer. I have a method that I am calling in another class, but I get the Fatal Error: Uncaught Error: Call to undefined function bla bla. Can anyone help me with this? Thanks in advance, and here is the code, the error is in the last method, on the while(alliesDefend >= 0)

    <?php
    class Duel{

public $_maxHealth;
public $_currentHealth = 0;
public $_specialAttack, $_mainAttack;
public $_specialChance, $deflectChance;
public $startHealth;
public $size1 , $size2;

function __construct($_size1, $_size2)
{
    $this->size1 = $_size1;
    $this->size2 = $_size2;
}

function baseNumberOne()
{
    $baseNumber = rand(1, 2) * $this->size1;
    return $baseNumber;
}


function baseNumberTwo()
{
    $baseNumberTwo = rand(1, 2) * $this->size2;
    return $baseNumberTwo;
}

function specialAttack(){
    $_specialChance = rand(0, 20);
    $_specialAttack = 0;

    if ($_specialChance < 10) {
        $_specialAttack = 0;
    } elseif ($_specialChance < 15) {
        $_specialAttack = (int) rand(0, 5);
    } elseif ($_specialChance <= 20) {
        $_specialAttack = (int) rand(5, 10);
    }
    return $_specialAttack;
}

function enemyAttack()
{
    $_mainAttackOne = $this->specialAttack() + $this->baseNumberOne();
    echo "The Enemy has attacked allied forces for $_mainAttackOne damage! <br/>";
    return $_mainAttackOne;

}

function alliesAttack()
{

    $_mainAttackTwo = $this->specialAttack() + $this->baseNumberTwo();
    echo "The allies have attacked enemy forces for $_mainAttackTwo damage! <br/>";
    return $_mainAttackTwo;

}

function startHealth()
{
    $startHealth = (int) (10 * $this->baseNumberOne());
    return $startHealth;
}

function startEnemyHealth()
{
    $startEnemyHealth = (int) (10 * $this->baseNumberTwo());
    return $startEnemyHealth;
}

function deflect(){
    $deflectChance = rand(1, 10);
    $deflect       = 0;

    if ($deflectChance < 5) {
        $deflect = 0;
        echo 'attack cannot be deflected<br/>';
    } elseif ($deflectChance > 5) {
        $deflect = (int) rand(0, 3);
        echo "attack is deflected for {$deflect} damage <br/>";
    }
    return $deflect;
}

function enemyDefend()
{
    $_currentHealth = $this->startHealth();

    $_currentHealth = $_currentHealth + $this->deflect() - $this->alliesAttack();

    echo "Enemies have has dropped to $_currentHealth HP <br/>";

    return $_currentHealth;

}

public function alliesDefend()
{
    $_currentHealth = $this->startEnemyHealth();

    $_currentHealth = $_currentHealth + $this->deflect() - $this->EnemyAttack();

    echo "Allies have has dropped to $_currentHealth HP <br/>";

    return $_currentHealth;

}

function war(){
    do{
        $this->enemyAttack();
        $this->alliesDefend();
        $this->alliesAttack();
        $this->enemyDefend();
    }while(alliesDefend() >= 0);
}
  } //end of class