this is my model

class ExchangeReportTime(models.Model):
    creator = models.ForeignKey('accounts.Account', on_delete=models.CASCADE, null=True, verbose_name=_('Creator'))
    create_time = models.DateTimeField(default=timezone.now)
    exchange = models.ForeignKey(BorseExchange, on_delete=models.SET_NULL, null=True,
                                 related_name='report_times')
    actual_fiscal_month = models.CharField(max_length=255, null=True, blank=True)
    fiscal_month = models.CharField(max_length=5, null=True, blank=True)
    fiscal_year = models.CharField(max_length=255, null=True, blank=True)
    is_fiscal_year_changed = models.BooleanField(null=True, blank=True)
    period_ending_date = models.CharField(max_length=15, null=True, blank=True)
    statement_key = models.IntegerField(null=True, blank=True)
    statement_type = models.CharField(max_length=50, null=True, blank=True)
    ...

fiscal_month and fiscal_year are string so i change types and query as below

    exchange = BorseExchange.objects.get(tse_code=exchange_number)
    last_12_season = exchange.report_times.filter(
        statement_type='InterimIncomeStatement',
        period_type='seasonally'
    ).annotate(
        fiscal_month_number=Cast('fiscal_month',IntegerField()),
        fiscal_year_number=Cast('fiscal_year',IntegerField()),
    ).order_by(
        '-fiscal_year_number', '-fiscal_month_number'
    ).distinct(
        'fiscal_month_number', 'fiscal_year_number'
    )[:records_count]
    print(last_12_season.values_list('id'))

but i give error:

django.core.exceptions.FieldError: Cannot resolve keyword 'fiscal_month_number' into field. Choices are: actual_fiscal_month, attachment_url, auditing, company_key, create_time, creator, creator_id, currency, exchange, exchange_id, fiscal_month, fiscal_year, html_url, id, is_empty, is_fiscal_year_changed, period_ending_date, period_type, publish_date, publish_time, report_items, scenario, statement_key, statement_type

where is the problem?

python3.6 and django 2.2.*