Hi,
Please download the latest version on our website (2.2.1), extract it and replace your administrator/components/com_hikashop/classes/filter.php file by the back/classes/filter.php of the package and try again.
If that doesn't help, we'll need a backend and FTP access.
If you edit your files via the menu Display->Views, you won't loose them when you update. And for files that you can't edit from there, you can use system plugin class overrides:
www.informit.com/articles/article.aspx?p=1858258&seqNum=8
That way you should never loose your modifications. It's also recommended to not just copy the whole class but instead load it from the original file and extend it in an override class <original class name>Override
That way you only redefine the functions you need to in it.