Sorry to hear of the problem you are having.
Please don’t share sensitive information on the forum like your purchase number as this is public forum so the information shared can be misused by others.
If you want to share any sensitive information with us then you can do so by adding them in the box having text “Click here to share private content. Only you and forum moderators will bee able see it.”?
Could you please try using the below shared theme on your site?
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You can fix 500 Internal server error on your site as described in the following page.
It seems you have already installed the Visual composer plugin on your site so just activate it from plugins section.
If you don’t find it in the plugins section then delete the plugin directory from your WordPress install on /wp-content/plugins/js_composer using FTP or cPanel file manager and then install the plugin.