taxonomies filter issue.

im trying to create a taxonomy filter in a widget but i cant get it do display region specific suburbs. i get a list of all regions and suburbs but i can not make it so that only the suburbs for the selected region are displayed, instead i get all suburbs in 1 list and all regions in another list as seen at my website here http://www.housewashingdirectory.co.nz/. Can anyone tell me what i am doing wrong or how to correctly configure my taxonomies so that when i pick the region in my first dropdown list the second dropdown list will only display the suburbs in that selected region.