If you suspect you have been hacked, first check your website files via FTP or File Manager.
If there are files dated later than the last one that you edited, check them for any unusual code.
Where possible, just overwrite them with the same files from your backup on your hard disk (or get your web designer to do this).
If it’s a WordPress website, and you don’t have a backup of those files on your hard disk, you may need to reinstall WordPress. If so see www.platywebs.com.au/hosting-wordpress-reinstall.php – but first ask us as we may have some shortcuts. We hope you have kept upgrading WordPress to the latest version.
It is a shock, you will feel violated, but there are ways to quickly restore your site.