OK so apparently Hostgator (urgh) have a 500mb limit for cpanel restores.
I rang them and they took 30 minutes of international call time to tell me I had to use FTP to restore the website - real experts these guys.
I managed to gain access to my FTP (FZ), apparently my entire email history is now deleted, and need to know how I restore my full website backup (tar.gz) via Filezilla.
I tried to drag across the zipped file - didn't work. I tried to drag an unzipped folder - didn't work. Website address just shows a directory. Backoffice doesn't exist 404.
I can't find a guid online. In hindsight, prestashop, hostgator and me being a tech idiot was a rookie mistake.
Help!