The Vacuum Breaker may have a hole in the side where a tamper proof locking screw is located.
If it does drill it out and it should unscrew.
You can then replace the vacuum breaker. get one that is freeze resistant.
If it is not a separate VB replace the hose bibb and VB. You should take cross connection as a serious problem that can effect the health and well being of your family and neighbors...
Not something that you can get away with....
Have a good read at this link!