WooCommerce Shipping zone issue

Hi,

*PLEASE READ FIRST BEFORE APPLYING - NO TIME WASTERS PLEASE*

I have a custom theme which is using the WooCommerce plugin, the shop sells over 400 products.
We have 4 different shipping zones depending on distance to calculate the shipping cost, some of the products can't be sold when the 4th shipping zone is applied.

We have setup shipping classes for these four categories and the products have been assigned to these classes, when a user orders only that item and falls within the 4th zone and goes to checkout WooCommerce gives an error and doesn't allow them to checkout which is correct, however when the user adds a second item to the cart which is allowed to be shipped to the 4th Zone it still allows them to checkout which shouldn't be the case.

I need to get this programatically sorted, so I'd need a hook for WooCommerce that checks the zone and then loops through the cart items to see if an item of those classes is added, if that's the case and the zone is the 4th it should throw a message and stop the user from placing the order.