Prepaid XBox Live Subscription cards are eaten by the service if your passport account has other premium Microsoft services attached.
Several XBox Live subscribers are in a suspended state, awaiting Microsoft’s help. The problem has been around since day one of the XBox 360 launch(I’ve been affected since 11/23/05). Depending on the duration of the service purchased and whether or not they purchased a headset, some users are out as much as $70. Also, misguided suggestions from customer support have resulted in people losing game saves.
Major Nelson(XBox Live representative) said on 12/1 that a fix was being tested. That was 16 days ago. http://forums.xbox.com/2/1145218/ShowPost.aspx#802691