First things first. If there is no backup, then the steps are:
- Go into your website database through phpMyAdmin (maybe you have something else)
- Find the table wp_options
- Replace addresses in sections siteurl and home address on your website
Now for the second. If you have outdated EAP plug-ins have not been updated, the crack can easily. After the restoration of the site, it is desirable to disable all plugins to check which of them have vulnerability. Just browse through the search engine. About the break any of your plugins on any note.
And Yes, not the fact that you aren't built into the site of any third-party js that is responsible for forwarding or just lying around the hacker that something is not required.