Assuming that you have already tried to reset the password on https://iforgot.apple.com/password/verify/appleid the easiest thing is to call Apple. I'm not sure which number would be better, but you can try to give them a call (US numbers):
1. Customer support: 1-800-275-2273
2. IPhone support:1-800-MY-IPHONE
If you have an Apple store nearby, it might be just as fast to go pay the store a visit.