Your best bet is to do as Gift3d suggested and call Xbox support. It is possible that your payment didn't clear. You might also want to check your email account that you have associated with your Live account. Most times if there is a problem, Microsoft will email you about it.
You should check your credit report first. It's weird for you to be a long time member and that suddenly happens. My guess is that you may have possibly lacked the funds at the time which is why your live gold isn't going through.
But still, do what the others said about customer service.