Thank you.
I see that your site is using Header Elements.
You can see the Elements list used on your site through Appearance > Elements.
I believe you’ll see a Header Element named “Global Page Headers” with “Location” set to pages. This is the one adding the title to your pages.
Edit this element if you want to change what it displays.
You’ll probably see something like this in its code area:
<h1>
{{post_title}}
</h1>
You can simply replace what it displays, or completely delete the Header Element if you don’t want to use it.