diff --git a/app/clients/cbc_proxy.py b/app/clients/cbc_proxy.py
index f46caaa40..67f796119 100644
--- a/app/clients/cbc_proxy.py
+++ b/app/clients/cbc_proxy.py
@@ -217,6 +217,9 @@ class CBCProxyVodafone(CBCProxyClientBase):
     def cancel_broadcast(
         self, identifier, previous_provider_messages, sent, message_number
     ):
+        # avoid cyclical import
+        from app.utils import format_sequential_number
+
         payload = {
             'message_type': 'cancel',
             'identifier': identifier,
@@ -225,7 +228,7 @@ class CBCProxyVodafone(CBCProxyClientBase):
             "references": [
                 {
                     "message_id": str(message.id),
-                    "message_number": message.message_number,
+                    "message_number": format_sequential_number(message.message_number),
                     "sent": message.created_at
                 } for message in previous_provider_messages
             ],
diff --git a/tests/app/clients/test_cbc_proxy.py b/tests/app/clients/test_cbc_proxy.py
index 4e0b491a6..93f7165ff 100644
--- a/tests/app/clients/test_cbc_proxy.py
+++ b/tests/app/clients/test_cbc_proxy.py
@@ -236,8 +236,8 @@ def test_cbc_proxy_vodafone_cancel_invokes_function(mocker, cbc_proxy_vodafone):
     MockProviderMessage = namedtuple('BroadcastProviderMessage', ['id', 'message_number', 'created_at'])
 
     provider_messages = [
-        MockProviderMessage(uuid.uuid4(), '0000007b', '2020-12-10 11:19:44.130585'),
-        MockProviderMessage(uuid.uuid4(), '0000004e', '2020-12-10 12:19:44.130585')
+        MockProviderMessage(uuid.uuid4(), 78, '2020-12-10 11:19:44.130585'),
+        MockProviderMessage(uuid.uuid4(), 123, '2020-12-10 12:19:44.130585')
     ]
     sent = '2020-12-10 14:19:44.130585'
 
@@ -275,12 +275,12 @@ def test_cbc_proxy_vodafone_cancel_invokes_function(mocker, cbc_proxy_vodafone):
     assert payload['references'] == [
         {
             "message_id": str(provider_messages[0].id),
-            "message_number": provider_messages[0].message_number,
+            "message_number": '0000004e',
             "sent": provider_messages[0].created_at
         },
         {
             "message_id": str(provider_messages[1].id),
-            "message_number": provider_messages[1].message_number,
+            "message_number": '0000007b',
             "sent": provider_messages[1].created_at
         },
     ]