private static string RandomString()
        {
            var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ3454323LMNOPQRSTUVWXYZ001206789";
            var stringChars = new char[4];
            var random = new Random();

            for (int i = 0; i < stringChars.Length; i++)
            {
                stringChars[i] = chars[random.Next(chars.Length)];
            }

            var finalString = new String(stringChars);
            return finalString;
        }
        private static string RandomString2()
        {
            var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
            var random = new Random();
            var result = new string(
                Enumerable.Repeat(chars, 4)
                          .Select(s => s[random.Next(s.Length)])
                          .ToArray());
            return result;
        }
        private static string RandomString3()
        {
            var chars = "ABWXYZ01234567IJKLMNOPQRSTUVWXYZ0123456789";
            var random = new Random();
            var result = new string(
                Enumerable.Repeat(chars, 4)
                          .Select(s => s[random.Next(s.Length)])
                          .ToArray());
            return result;
        }
        private static string RandomString4()
        {
            var chars = "ABWXYZ01234567IJKLMNOPQRSTUVWBWXYZ0120123456789";
            var random = new Random();
            var result = new string(
                Enumerable.Repeat(chars, 4)
                          .Select(s => s[random.Next(s.Length)])
                          .ToArray());
            return result;
        }