RE: IIS hosted Web service using an AX wcf service: The Target principle name is incorrect

I see that you're not disposing your service clients. To be sure that that's not the cause, please fix your code and restart the AOS.

By the way, you'll make your code much simpler and more readable if you don't always use fully qualified names. It's not needed. For example, instead of

AxCreditLimitService.CallContext callContext = new AxCreditLimitService.CallContext();

you can simply write

CallContext callContext = new CallContext();

You just have to add an extra using statement:

using AxCreditLimitService;