diff --git a/cleanowners.py b/cleanowners.py
index a700db8..f7fc22f 100644
--- a/cleanowners.py
+++ b/cleanowners.py
@@ -94,8 +94,9 @@ def main():  # pragma: no cover
                 if not dry_run:
                     # Remove that username from the codeowners_file_contents
                     file_changed = True
-                    codeowners_file_contents = codeowners_file_contents.decoded.replace(
-                        f"@{username}", ""
+                    bytes_username = f"@{username}".encode("ASCII")
+                    codeowners_file_contents_new = (
+                        codeowners_file_contents.decoded.replace(bytes_username, b"")
                     )
 
         # Update the CODEOWNERS file if usernames were removed
@@ -106,7 +107,7 @@ def main():  # pragma: no cover
                     title,
                     body,
                     repo,
-                    codeowners_file_contents,
+                    codeowners_file_contents_new,
                     commit_message,
                     codeowners_filepath,
                 )
@@ -175,7 +176,12 @@ def get_usernames_from_codeowners(codeowners_file_contents):
 
 
 def commit_changes(
-    title, body, repo, codeowners_file_contents, commit_message, codeowners_filepath
+    title,
+    body,
+    repo,
+    codeowners_file_contents_new,
+    commit_message,
+    codeowners_filepath,
 ):
     """Commit the changes to the repo and open a pull reques and return the pull request object"""
     default_branch = repo.default_branch
@@ -184,10 +190,9 @@ def commit_changes(
     front_matter = "refs/heads/"
     branch_name = "codeowners-" + str(uuid.uuid4())
     repo.create_ref(front_matter + branch_name, default_branch_commit)
-    repo.create_file(
-        path=codeowners_filepath,
+    repo.file_contents(codeowners_filepath).update(
         message=commit_message,
-        content=codeowners_file_contents.encode(),  # Convert to bytes object
+        content=codeowners_file_contents_new,
         branch=branch_name,
     )
 
diff --git a/test_cleanowners.py b/test_cleanowners.py
index 6ffcc1b..792ce1a 100644
--- a/test_cleanowners.py
+++ b/test_cleanowners.py
@@ -24,7 +24,8 @@ def test_commit_changes(self, mock_uuid):
         mock_repo.default_branch = "main"
         mock_repo.ref.return_value.object.sha = "abc123"  # Mock SHA for latest commit
         mock_repo.create_ref.return_value = True
-        mock_repo.create_file.return_value = True
+        mock_repo.file_contents.return_value = MagicMock()
+        mock_repo.file_contents.update.return_value = True
         mock_repo.create_pull.return_value = "MockPullRequest"
 
         title = "Test Title"
@@ -45,12 +46,7 @@ def test_commit_changes(self, mock_uuid):
         mock_repo.create_ref.assert_called_once_with(
             f"refs/heads/{branch_name}", "abc123"
         )
-        mock_repo.create_file.assert_called_once_with(
-            path="CODEOWNERS",
-            message=commit_message,
-            content=dependabot_file.encode(),
-            branch=branch_name,
-        )
+        mock_repo.file_contents.assert_called_once_with("CODEOWNERS")
         mock_repo.create_pull.assert_called_once_with(
             title=title,
             body=body,