If you have used the zip/post code restriction feature for your store, and when you do a test order, the zip/post codes are not restricting the areas you have setup, then you may have extra shipping rates setup.
These shipping rates can be default shopify rates, or another app or carrier service. They could also be other Better Shipping rates if you have multiple rates setup using the same Shipping Zone.
The first thing to check is your ShopifyAdmin->Settings->Shipping and delivery->General->Manage page under the Shipping Zones section.
Under the relevant shipping zones (e.g. "Domestic") you can check if you have multiple services installed. The Better Shipping service is called "Better Shipping App rate estimates". If you have other services installed along side the Better Shipping service in the same shipping zone, then that is most likely the problem. Better Shipping can restrict its own rates via zip/post code, but we can't restrict other services.
If you want to restrict your customers to specific shipping addresses, then you must use Better Shipping exclusively for that shipping zone. To do this, just delete all of the other shipping services under the shipping zone using the "Edit" link next to the relevant shipping zone. Then delete the services and click "Save".
You can then do a test order and see if your zip/post codes are restricting properly.
The next thing to check is to see if you have multiple shipping rates to the same shipping zone within the Better Shipping app. On the main shipping rate page, you can see a list of your Better Shipping shipping rates and their respective shipping zones.
You can see in the image above, there are two shipping rates, and they both have the same shipping zone. You must make sure that both rates have the same zip code restrictions. If they don't then one of the rates will restrict to the correct areas, but the other rate will still be available to the zip codes that you tried to restrict.
You can edit the rates and double check you have the same settings by clicking on the name of the shipping rate.
If your shipping rates are still not restricting, then as always, please don't hesitate to email us at email@example.com so we can help you out!