when they call your number, voda is probably routing the call to Optus or Telstra, thinking your mob no resides on one of those networks, resulting in a disconnected error (and you can tell which depending on the lady voice and message).
All they have to do is tell their system that your phone no is on 3/Hutchinson and not optus/telstra and it'll route the calls accordingly.
That's if it is what I think it is. You could probably ring 3 and log a fault that you can't receive calls from anyone on the Voda network. (Have you had other voda people attempt to call you?). The fault is with your number, so as their customer, 3 should be able to take it on board and contact the appropriate peopel within vodafone to ahve the problem corrected. Your brother/etc don't really have any legal/other jurisdiction to have anything about your number changed as it is not their own.
If the problem is not as described then I'd need more info.