Last I checked, which was about two weeks ago, the law was that the 28 day period starts when your application arrives in the hands of the CFC and not when they decide to pull it from the pile and dust it off and start work on it. A legal statute I do believe. It's one of the reasons why it's advisable to send registered mail and to pay by credit card or other method you can track and verify, so that when it arrives and they take your money you can call and remind them that it means they're now already processing the application.
I say that you should call them. If you have a definite date they received it, such as a postal tracking number, or billing to your credit card, you can mention that date and get them to verify it. Be polite, but as of now there's no legal reason why the wheels are not spinning. At least that's assuming something genuine hasn't come up, like someone with the same name who has a criminal record, or a previous tenant who's still registered as living at your address and mucking things up, etc.