Django TestCase: can't see record updated in test db

I'm testing a function in my project. The function modifies some records in my test db. I'm interested to see if a specific record was updated. I call my method inside my test_function and after that looking for the record. It seems the record wasn't updated, but the function (with some logs) tells me it was!

I created my TestCase class using both TestCase and TransactionTestCase, but none of them worked. I'm usign Django 2.2

class HostTestCase(TransactionTestCase):

    def setUp(self):
        task = Task.objects.create(name='do_backup', description="")
        for i in range(1, 17):
            if i in [4, 7, 9, 11, 12, 14, 15]:
                host = Host.objects.create(
                name="test_sbb{}".format(i),
                mac_address="asgsb{}".format(i),
                remote_address="mock-server{}:4010".format(i)
            )
                if i in [11, 14, 15]:
                    host.last_seen_at = timezone.now()
                    host.save()
                if i in [9, 12, 15]:
                    task_assigned = Host_Task.objects.create(host=host, task=task, status="IDLE")
                elif i in [4, 7, 11, 14]:
                    task_assigned = Host_Task.objects.create(host=host, task=task, status="WORKING_CREATION")
            else:
                if i != 16:
                    host = Host.objects.create(
                        name="test_sbb{}".format(i),
                        mac_address="asgsb{}".format(i),
                        remote_address="mock-server{}:4010".format(i),
                        get_backup=False
                    )
                    if i in [8, 10, 13]:
                        host.last_seen_at = timezone.now()
                        host.save()
                    if i in [3, 6, 10, 13]:
                        task_assigned = Host_Task.objects.create(host=host, task=task, status="WORKING_CREATION")
                else:
                    host = Host.objects.create(
                    name="test_sbb{}".format(i),
                    mac_address="asgsb{}".format(i),
                    remote_address="mock-server:4010"
                )
                    host.last_seen_at = timezone.now()
                    host.save()
            influx = InfluxDB(host)
            # create new db
            influx.create_database()
            write_mock_data(influx, i)

    def tearDown(self):
        for i in range(1, 17):
            host = Host.objects.filter(name="test_sbb{}".format(i)).first()
            influx = InfluxDB(host)
            influx.client.drop_database("{}_metrics".format(host.name))
            print("DB {}_metrics dropped".format(host.name))

    def test_do_backup_OK(self):
        host = Host.objects.filter(name="test_sbb16").first()
        task = Task.objects.filter(name="do_backup").first()
        task_assigned = Host_Task.objects.create(host=host, task=task, status="IDLE")
        task_manager = TaskManager()
        task_manager.do_backup()
        task_assigned.refresh_from_db()
        self.assertEqual(task_assigned.status, "WORKING_CREATION")

The do_backup should modify only the Host_Task object with host = test_sbb16 and that task, updating the status to "WORKING_CREATION, instead the status remains "IDLE"