You cannot access the Control values in the Web Methods. You need to pass these values using jQuery Ajax to the web methods.
Refer:
- How to return multiple values from WebMethod to jQuery using AJAX in ASP.Net
In the above link i am assigning the values to span control same way you can apply the response data to Textboxes.
If you are using Server side TextBox controls then you need to write the JQuery code like this to assign the value in it.
$('[id*=txtName]').val('Some Text');