RossMitchell

Instead of through the customizer, you will have a better time changing themes etc through the old path: Dashboard > Appearance > Themes and so on.
Or you could change to a different browser.

Sorry, your website that displays is not a WordPress website, the code shows the generator is “1&1 MyWebsite”, does this ring a bell with you ?

The code is:
<meta name="generator" content="1&1 MyWebsite">
Other signs are that your within website menu links are “.html” files.

What you are showing is a relic website at the same address, once you remove its visibility the WordPress website will become visible.

So for a start, I suggest you rename “index.html” to something else like “old.html”, no need to rename “insurances.html” or “doctor.html”. Now you will be able to get to work.

I am curious as to what you want to achieve ? What security situations do you want to defend against ?

If the WordPress core were able to encrypt the data that was stored in the tables, then it would also have to be able to decrypt it too, so the encrypt and decrypt keys would be in the website somewhere. So what security would you have achieved ?

I have thought of other security illusions too. Like the database user is configured to have all privileges, surely this is excessive, like create table ability is only required for install or maintenance, so why not have two users, the normal WordPress runtime would not need table create say. But this achieves nothing, you have to have database update capability anyway, with it malicious code can destroy a website, so it does not matter.

Have you asked in the support forum for this plugin ?
Looks like here: https://revolution.themepunch.com/

Since the volunteers here do not have access to this code, it is expected that you get support from the vendor.

I am curious as to your contractual relationship and obligations with this company.
You have said that they refuse to support your site, but then continue to say that the would expect to be paid for making changes.
If it were my work, I would expect to be acknowledged for my authorship, on what grounds do you want it removed ?

The validator found that your page has errors. One is that there are TWO “body” elements, this is never correct. You need to fix this problem(s), either seek support from your theme author, or create a child theme and fix it yourself.

Changing css is not a solution.

Create a child theme and make a custom page template for displaying categories, details here:
http://codex.wordpress.org/Child_Themes
https://developer.wordpress.org/themes/basics/template-hierarchy/

It would help us help you if you included a link to your site.

Without having your circumstances in front of me, you could use your browser inspector to view the html + css of your web pages, and put a phrase of custom css in your customizer along the lines of:

"some list of classes" {
 display:none;
}