I've enrolled online on the 5th of february as well and I got my invitation by mail on the 26th and by letter on the 27th.
My test is the 10th of March.
And if you want to contact them I think it's best to do it by telephone, I guess these days they're very busy with all the testing and so on...
Don't mean to discourage you, from what I've heard they invite everybody that has registered.