403 forbidden error; checked everything I can

I’m getting a 403 forbidden error on every part of my wordpress website. I can’t even get to wp-admin.
On top of that I get this error: “Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.”

What I already checked:
– user server login settings
– permissions
– DNS IP address
– htaccess file
– updating wordpress

htaccess file looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

I’m out of solutions and can’t find any other ones on the interwebs. Does anyone here have some experience with the same problem or any solutions?

Much thanks in advance!