It's also possible that you have a persistent cookie (probably from Budget) on your computer that automatically fills in the Fastbreak account number when you hit the Budget site, no matter whether you enter directly or from a third party website.

One way to check is to attempt a booking with Budget on a different computer and see if the same problem occurs.

If it doesn't, check the cookies on your computer for any from Budget and delete them, reboot, and try again (or you can just delete all cookies, but that may cause you to lose some other "remember me" fill-ins).