I agree with the poster who said to make sure your email address is set to your Live account. I get emails everytime my son does a $5.00 download. That's a nice feature to have when you've got 2 Xbox's and your kid thinks it's okay to pay the $5.00 for both systems! UGGGHHHH
For us, the $50 was automatically charged when ours expired and I got an email telling me in advance that they'd be taking it out and when they'd do it, then I got another one when they actually took the money.