PDO query using parameters does noct work

Question

I have a problem with a PDO query. I am trying to update data in an existing DB entry.

This is the SQL query I am using. The missing parameters are passed via the $arguments array.

$sql = "UPDATE user SET vorname = :vorname, nachname = :nachname, plz = :plz, strasse = :strasse, hausnummer = :hausnummer WHERE id= :id";  // SQL to update category
   print( "SQL 2: $sql");

The query itself takes place in this function.

function pdo(PDO $pdo, string $sql, array $arguments = null){
  if (!$arguments) {
    return $pdo->query($sql);
  }
  $statement = $pdo->prepare($sql);
  $statement->execute($arguments);
  return $statement;
}

So far it runs error free, but after sending it the entry is not updated.

 pdo($pdo, $sql, $arguments);  

When I output $sql I see the following....

SQL 2: UPDATE user SET vorname = :vorname, nachname = :nachname, plz = :plz, strasse = :strasse, hausnummer = :hausnummer WHERE id= :id

Does anyone have an idea what I am doing wrong?