Unless I am missing something completely you are utilizing ASP.NET MVC. The MVC framework is not compatible with .asmx as MVC routing will intercept a .asmx request.
To clarify,
public ActionResult AddCpty
is how you declare an Action within an MVC controller in the ASP.NET MVC Framework.
Based on your question, I would suggest you read more on what it is you are trying to do/accomplish as trying to explain how MVC routing works may add to the confusion.
My suggestion is to drop the notion of creating .ASMX web services (unless you have a need to create it in that manner) and look at Web API as Web API will allow you to more easily use MVC code for a web service.
Web API - Google Search[
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ASP.NET MVC to .ASMX[
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ASP.NET MVC - Google Search[
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