Effective technology stack for automating website tasks

I am trying to automate some processes that I normally do through a browser. For example, logging into a Wordpress page and editing a post.

I am most familiar with C++. Second most familiar is C#, however its not a close second, C++ wins by far. I am unfamiliar with web development and the technologies used.

Currently what I use is libCurl to login to my Wordpress. However I encountered a problem when trying to automatically update posts. The post parameters sent when updating the post are created through javascript. I've seen stuff like PhantomJS or CasperJS, and that seems to be what I want, however I don't know how to interface that with my C++ application.

In terms of C#, the WebBrowser class seemed promising as it was a headless browser. It seems its exactly Internet Explorer stripped of all UI and user interactivity. This didnt work for me because, although the Javascript functionality was in place, proxies didn't work well (you cant simultaneously use multiple proxies).

To summarize: to have the most functionality, what languages/libraries/technologies are good for essentially having my own headless web browser? There must be website automation tools that can help me.