Sorry to hear you ran into problems.
First, let me clear something up: an upgrade to pro is not obligatory: the plugin states that you should check your CSS and JS files for hardcoded http links, which cannot be fixed dynamically. But if you don’t want to do this yourself, you can get the pro plugin to do this for you.
We have tried to make this as easy is possible, but with over 800 000 installs there are bound to be some special cases. We have created an extensive knowledge base on https://really-simple-ssl.com where every issue we have encountered is described as clearly as possible. Additionally, you can always request support on https://really-simple-ssl.com/support, which we are happy to give.
In your case the hardcoded http links in CSS or JS files are probably causing your issue. I have written an article how you can find these manually:
https://really-simple-ssl.com/knowledge-base/how-to-track-down-mixed-content-or-insecure-content/
Regarding the .htaccess redirect: if you have enabled the .htaccess 301 redirect in settings/ssl, and it wasn’t enforced, the redirect possibly couldn’t be created because a possible redirect loop was detected.
If your site force redirects back to http, this might cause a loop when a redirect is enabled. Without more information it is hard to say why this didn’t work for you. If you put in a support request we can help you with this.
