C# codepath doesn't return value altough it is reached

Question

I have this recursive async method:

 public Task<string> CreatePasswords(string keys, char[] alphabet, string passwordHash256, int expectedLength, bool done)
    {
        return Task.Run(() =>
        {
            if (HashPassword(keys) == passwordHash256)
            {
                Console.WriteLine(HashPassword(keys));
                Console.WriteLine(passwordHash256);
                Console.WriteLine(keys.ToString());
                return keys.ToString();
            }
            if (keys.Length > expectedLength || done == true)
            {
                return "not found";
            }
            for (char c = alphabet[0]; c <= alphabet[alphabet.Length - 1]; c++)
            {
                 CreatePasswords(keys + c, alphabet, passwordHash256, expectedLength, done);
            }
            return "not found";
        });
    }

If the hash of the keys equals the given passwordHash256 the program shoul return the keys as a string and stop then. The problem I have with this code is that altough the hash of the keys equals the passwordHash256 the keys don't get returned. The return value is always not found.

This is how I call the Method:

public async Task<string> FindPasswordInHash(string passwordHash256, int length, char[] alphabet)
{
    var stuff = await CreatePasswords(string.Empty, alphabet, passwordHash256, length, false);
    return stuff;

}

Sample data:

length: 5
alphabet: aehy
hash: ef7c77aedd4e9f66044feabadc6057f7821004489a80b69b8dd2682888fa90b3

PasswordHash:

  public string HashPassword(string password)
{
    using (SHA256 mySHA256 = SHA256.Create())
    {
        var hash = mySHA256.ComputeHash(Encoding.UTF8.GetBytes(password));
        string result = "";
        for (int i = 0; i < hash.Length; i++) result += hash[i].ToString("X2");
        return result.ToLower();
    }
}