public IActionResult Deposit(DepositWithdrawViewModel model)
        {
            var customers = _bankRepository.GetListOfCustomers();

            var account = customers.SelectMany(i => i.Accounts.Where(x => x.Accountnumber.Equals(model.Account.Accountnumber))).SingleOrDefault();

            if (account == null)
            {
                ModelState.AddModelError("", "The account number doesn't exist.");
                model.Account = null;
                return(View("DepositWithdraw", model));
            }
            else
            {
                _bankRepository.DepositAccount(model.Sum, account);
                model.Account.Balance = account.Balance;

                return(View("DepositWithdraw", model));
            }
        }