WP SUper Cache Failed Install

Hello,
I recently installed the WP SuperCache plugin, howevr it failed its set up, and i recieve the following error:
Warning! Could not update /homepages/23/d679830818/htdocs/app679837448/wp-config.php! WPCACHEHOME must be set in config file.

Warning! /homepages/23/d679830818/htdocs/app679837448/wp-content/advanced-cache.php does not exist or cannot be updated.

1. If it already exists, please delete the file first.
2. Make /homepages/23/d679830818/htdocs/app679837448/wp-content writable using the chmod command through your ftp or server software. (chmod 777 /homepages/23/d679830818/htdocs/app679837448/wp-content) and refresh this page. This is only a temporary measure and you’ll have to make it read-only afterwards again. (Change 777 to 755 in the previous command)
3. Refresh this page to update /homepages/23/d679830818/htdocs/app679837448/wp-content/advanced-cache.php
If that doesn’t work, make sure the file /homepages/23/d679830818/htdocs/app679837448/wp-content/advanced-cache.php doesn’t exist:
1. Open /homepages/23/d679830818/htdocs/app679837448/wp-content/plugins/wp-super-cache/advanced-cache.php$wp_cache_file in a text editor.
2. Change the text CACHEHOME to /homepages/23/d679830818/htdocs/app679837448/wp-content/plugins/wp-super-cache/
3. Save the file and copy it to /homepages/23/d679830818/htdocs/app679837448/wp-content/advanced-cache.php and refresh this page.
Cannot continue… fix previous problems and retry.

Unfortunately i am not using my own web server – i am using 1 & 1 hosting, so dont have the files it is asking for.
I cannot uninstall/ deactive the plugin as i am taken to a page with the following error.

Error thrown

Call to undefined function wpsc_get_realpath()

This is also now stopping me getting to my avada theme options as i recieve the ERROR THROWN page on that too.

I cannot work out how to fix – please help!