Letter have multliple rates, the agregate number was not taking that into account for the usage page.

app/main/views/dashboard.py

@@ -389,8 +389,8 @@ def calculate_usage(usage, free_sms_fragment_limit):
 
     letters = [(breakdown["billing_units"], breakdown['letter_total']) for breakdown in usage if
                breakdown['notification_type'] == 'letter']
-    letter_sent = 0 if len(letters) == 0 else letters[0][0]
-    letter_cost = 0 if len(letters) == 0 else letters[0][1]
+    letter_sent = sum(row[0] for row in letters)
+    letter_cost = sum(row[1] for row in letters)
 
     return {
         'emails_sent': emails_sent,

tests/app/main/views/test_dashboard.py

@@ -777,11 +777,12 @@ def test_usage_page_with_letters(
     assert 'April' in table
     assert 'February' in table
     assert 'March' in table
-    assert '£18.94' in table
+    assert '£20.59' in table
     assert '140 free text messages' in table
     assert '£20.30' in table
     assert '1,230 text messages at 1.65p' in table
     assert '10 letters at 31p' in table
+    assert '5 letters at 33p' in table
 
 
 def test_usage_page_with_year_argument(

tests/conftest.py

@@ -2288,6 +2288,14 @@ def mock_get_billable_units(mocker):
                 'notification_type': 'letter',
                 'rate': 0.31,
                 'billing_units': 10
+            },
+            {
+                'month': 'February',
+                'international': False,
+                'rate_multiplier': 1,
+                'notification_type': 'letter',
+                'rate': 0.33,
+                'billing_units': 5
             }
         ]