Learn how to do them yourself. It's much easier, and you know it has been done.
If you get stopped by customs/special branch/immigration and they claim that they never got your notification, they aren't likely to accept the "The guy in the tower was supposed to do it!" defence.
They will point out that it is your responsibility to ensure that it is done, and not the guy in the tower.
Even if the guy in the tower does it correctly, and customs/special branch/immigration lose the form, you have no way of proving it was sent.
If you do it yourself, you can keep a copy of the fax confirmation page with you and politely wave it in their face while asking for an apology or their managers name.
dp