It is not quite possible to trace a new number from an old number. You need to go to the telephone department and inquire about the same. Usually, the telephone department does not entertain such kind of cases. They cannot give out personal information about people to anybody. You may try to explain the reason why you require the new number and explain that it is an emergency. In case the telephone department does not help, you can go to your nearest police station. You can register a complaint against your ex-girlfriend and the police will do their best to find out where she is. You can find out with some common friends as well.
