How to read cust ID from .net code

Hi,

Have a scenario wherein I need to read sales order XML file using SalesOrderService service. XML needs to be modified to include some fields like customer id, customer group etc before feeding it to the service. For this I am calling the service from .NET. I need to find out Customer ID using Shipping address(ZIP, STATE, ADDRESSLINE1 etc) from .NET code.

Tried to read this using read operation from CustomerService. As I dont have the entity key which is accountnum(Customer ID) in this case this is not working.

Please suggest me any other way of reading the customer id using shipping address from .NET. I am using AX2012

Thanks in advance.