If you want to fix it yourself, I'd do this:
change the database password (ask the googles for help on this process)
change your FTP passwords
change your email passwords
change your hosting passwords
use strong passwords throughout
use the Dashboard, Update to reinstall WP 4.8
also update any plugins or themes noted there
check the .htaccess file for changes (make a new one)
reinstall all themes (download files from theme home and upload to the proper folder via FTP or cPanel)
do the same for all plugins
remove/delete any plugins/themes you don't need or use
look for any posts/pages you didn't create; delete them
Long-term, keep everything updated. This is a bit of work, but can be done with some knowledge (and you can also ask the googles how to do most things). If you aren't comfortable doing all that, then find a consultant that will help you. It will cost, as the whole process is time-consuming.
Another option is to start from scratch - kill the old site completely (delete database and files) and reinstall everything. But that's not usually possible with most established sites.
This hack/attack can be recovered from...I've done it before. It just takes a bit of time and knowledge to do it. If you have content that must be saved, it will be a bit more complex, but still doable.
Good luck!
Added
And since you have a WooCommerce site, go through each product listing and remove anything that doesn't belong (could be some code inserted in a bogus product).