fatal error when installing them

After installing a new them in stories section, I received this error: Fatal error: Call to undefined function wp_get_theme() in /home/dirtypay/public_html/mountainxtasy.com/stories/wp-content/themes/opulus-sombre/functions.php on line 7 I now can not log in to stories. The blog and articles section are fine and I can still do anything I want there. I do not have ftp access to the site (they are working on that!!) I only have an admin template that allows me to do limited things to the site. The blog and article sections are version 3.7.1 I forgot to upgrade this section prior to downloading theme. It should be the previous version. Any help would be appreciated.