Level.cs

Next in Level.cs find the following in the UpdateEnemies method

// Touching an enemy instantly kills the player
if (enemy.BoundingRectangle.Intersects(Player.BoundingRectangle))
{
    OnPlayerKilled(enemy);
}

And change it to the following:

if (enemy.IsAlive && enemy.BoundingRectangle.Intersects(Player.MeleeRectangle))
{
    if(Player.isAttacking)
        OnEnemyKilled(enemy, Player);
}

Now under the UpdateEnemies method add a new method:

private void OnEnemyKilled(Enemy enemy, Player killedBy)
{
    enemy.OnKilled(killedBy);
}

And that's it! Give it a try and see if you can finally kill those enemies!