The reason why my website was still redirecting to HTTPS was because of a plugin. The plugin was disabled, by emptying the database cell which contains the “active plugins”, but still it was overruling every WordPress setting so it seemed. Every setting in wp-config.php which should overrule database settings or disabling/removing cache, didn’t worked out. I tried literally everything which can be found on most blogs, the WordPress documentation etc.
But moving all plugins from wp-content/plugins to a temporary folder called wp-content/plugins-backup helped me to reach the admin page and by moving the plugins back to the wp-content/plugins folder, one by one (or a few at a time), helped me figuring out which plugin was the problem.