diff --git a/app/service/rest.py b/app/service/rest.py
index 86908a92b..a22373b02 100644
--- a/app/service/rest.py
+++ b/app/service/rest.py
@@ -2,7 +2,10 @@ import itertools
 from datetime import datetime
 
 from flask import Blueprint, current_app, jsonify, request
-from notifications_utils.letter_timings import letter_can_be_cancelled
+from notifications_utils.letter_timings import (
+    letter_can_be_cancelled,
+    too_late_to_cancel_letter,
+)
 from notifications_utils.timezones import convert_utc_to_bst
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm.exc import NoResultFound
@@ -473,9 +476,17 @@ def cancel_notification_for_service(service_id, notification_id):
         raise InvalidRequest('Notification cannot be cancelled - only letters can be cancelled', status_code=400)
     elif not letter_can_be_cancelled(notification.status, notification.created_at):
         print_day = letter_print_day(notification.created_at)
-
+        if too_late_to_cancel_letter(notification.created_at):
+            message = "It’s too late to cancel this letter. Printing started {} at 5.30pm".format(print_day)
+        elif notification.status == 'cancelled':
+            message = "This letter has already been cancelled."
+        else:
+            message = (
+                f"We could not cancel this letter. "
+                f"Letter status: {notification.status}, created_at: {notification.created_at}"
+            )
         raise InvalidRequest(
-            "It’s too late to cancel this letter. Printing started {} at 5.30pm".format(print_day),
+            message,
             status_code=400)
 
     updated_notification = notifications_dao.update_notification_status_by_id(
diff --git a/tests/app/service/test_rest.py b/tests/app/service/test_rest.py
index f80063dd6..b16ab5fb8 100644
--- a/tests/app/service/test_rest.py
+++ b/tests/app/service/test_rest.py
@@ -3445,6 +3445,7 @@ def test_cancel_notification_for_service_raises_invalid_request_when_letter_is_i
     notification_status,
 ):
     sample_letter_notification.status = notification_status
+    sample_letter_notification.created_at = datetime.now()
 
     response = admin_request.post(
         'service.cancel_notification_for_service',
@@ -3452,7 +3453,13 @@ def test_cancel_notification_for_service_raises_invalid_request_when_letter_is_i
         notification_id=sample_letter_notification.id,
         _expected_status=400
     )
-    assert response['message'] == 'It’s too late to cancel this letter. Printing started today at 5.30pm'
+    if notification_status == 'cancelled':
+        assert response['message'] == 'This letter has already been cancelled.'
+    else:
+        assert response['message'] == (
+            f"We could not cancel this letter. "
+            f"Letter status: {notification_status}, created_at: 2018-07-07 12:00:00"
+        )
     assert response['result'] == 'error'