W3 Total Cache Error after multiple host ‘fixes’

Thank you in advance for taking the time to read this.

I updated WordPress to version 4.7.2 from the WordPress dashboard, after which my dashboard content disappeared. I was still logged in, could see my details at the top of the screen, but couldn’t navigate without getting an error (500). My site at this point was still working fine, but I couldn’t get back onto my dashboard. I cleared cookies etc, tried logging back in through my admin url (not the default), but still got the 500 error message. (www.jubileefireworks.com)

I contacted my host (One) who advised me to manually deactivate my plugins from my host panel by removing them completely from the PHP panel. After I did so, much of the text on my website turned to code, and I still couldn’t log in to my WordPress dashboard.

I was then advised by One to switch on PHP errors and contact them after 20 minutes when error messages appeared. After 90 minutes no messages appeared and I contacted them again. I was advised to update WordPress manually (wish I had done so at the start), which I did in Filezilla. Again no change.

Contacted One again who advised me to enable debugging, and manually update WordPress again. No change.

This time One advised me they believed my theme was causing an issue and I should switch to twentythirteen via my PHP panel. Still couldn’t log in.

I was then told to rename my plugin folder ‘plugin1’. No change. I was then told to delete the W3 Total Cache plugin from the Plugins folder in Filezilla. And now I get the following message;

W3 Total Cache Error: some files appear to be missing or out of place. Please re-install plugin or remove /customers/6/c/2/jubileefireworks.com/httpd.www/wp-content/advanced-cache.php.W3 Total Cache Error: some files appear to be missing or out of place. Please re-install plugin or remove /customers/6/c/2/jubileefireworks.com/httpd.www/wp-content/object-cache.php. Warning: Cannot modify header information – headers already sent by (output started at /customers/6/c/2/jubileefireworks.com/httpd.www/wp-content/advanced-cache.php:23) in /customers/6/c/2/jubileefireworks.com/httpd.www/wp-includes/pluggable.php on line 1179

Clearly I’m a novice, but I follow step-by-step instruction well. Something corrupted the initial update and every single piece of advice I’ve had from One so far either hasn’t solved anything or has caused additional issues.

There is nobody to phone there, and the chat reps are likely just bots with perhaps a passing human every now and then If someone would be kind enough to provide me with some simple (sorry, I know) instructions or advice on how I can get back into my dashboard where I can hopefully start solving things, I would truly appreciate it. I wish I had just come here first while my site was still functioning correctly.

Kindest regards,
PJ