internal bool SaveNewPayment(Guid ID, Guid CreditID, decimal _paymentAmmount, DateTime dateTime)
        {            
            bool flag = true;
            using (SqlConnection _connection = new SqlConnection(_connectionString))
            {
                _connection.Open();
                SqlTransaction _sqlTrans = _connection.BeginTransaction();
                SqlCommand _sqlCommand = _connection.CreateCommand();
                _sqlCommand.Transaction = _sqlTrans;
                try
                {
                    string _query = String.Format("INSERT INTO Payments (ID, CreditsID, Amount, PaymentDate) VALUES"+
                        "('{0}', '{1}', '{2}', '{3}')", ID, CreditID, _paymentAmmount, dateTime);
                    _sqlCommand.CommandText = _query;
                    _sqlCommand.ExecuteNonQuery();

                    _query = String.Format("UPDATE Cretits SET Balance = (Balance - {0}) WHERE ID = {1}", _paymentAmmount, CreditID);
                    _sqlCommand.CommandText = _query;
                    _sqlCommand.ExecuteNonQuery();

                    _sqlTrans.Commit();
                }
                catch(Exception)
                {                    
                    _sqlTrans.Rollback();
                    flag = false;
                }
                finally
                {                    
                    if (_connection.State == System.Data.ConnectionState.Open)
                        _connection.Dispose();
                }
            }
            return flag;
        }

dateTime.ToString("yyyy-MM-dd HH:mm:ss")