using System.Collections.Generic;
public class GetCreditCardListResponseCache
public List<CreditCardListResponseCache> Families { get; set; }
public class CreditCardListResponseCache
public List<CreditCardListResponse2Cache> CreditCards { get; set; }
public class CreditCardListResponse2Cache
public string AccountIndex { get; set; }
public string CardNumber { get; set; }
public static void Main()
var cacheCreditCardList = JsonConvert.DeserializeObject<GetCreditCardListResponseCache>("{\"Families\":[{\"CreditCards\":[{\"AccountIndex\":\"5\",\"CardNumber\":\"4730148900110111\"},{\"AccountIndex\":\"6\",\"CardNumber\":\"4730148900110210\"}]},{\"CreditCards\":[{\"AccountIndex\":\"7\",\"CardNumber\":\"5444828900066116\"},{\"AccountIndex\":\"8\",\"CardNumber\":\"5444828900066215\"}]}]}");
var creditCard = cacheCreditCardList.Families.SelectMany(a => a.CreditCards).Where(b => b.AccountIndex == "8").FirstOrDefault();
var logdata = JsonConvert.SerializeObject(creditCard);
Console.WriteLine(logdata);