You can register again using a new can if you really need to do it today or can't call up next week to get your existing numbers. Simply go to register on humanservices website, and apply to register for centrelink online services, and then choose "I have a crn but don't know it". Someone will then get your claim and link it to your existing file. It isn't the preferred thing to do - if you can't find your CAN, the best thing would be to call up on Tuesday to get your existing one. But the option is there to re-register. You only need minimal registration to apply for a payment