Maria,
Sorry for the trouble there. It looks like someone has created a theme called Agency and submitted it to WordPress.org. WordPress checks for theme updates based on the name and version number that is specified in the themes style.css file. If a different theme with the same name has a higher version number at WordPress.org, then it will indicate there is an update, even if it’s not the same theme.
There are two ways around that. You can keep the version that you were able to revert to and just remember to not use the updater for the theme.
The second option is to download the current version of the theme from the right hand side here and upload it to your site. That will give you the current version of the theme. It includes a separate update script that will load updates from here instead of wordpress.org. That way you can update in the future and not switch themes in the process.
To install the updated theme, download it. Then unzip the agency.zip file and rename the folder there agency-update and then zip it back up. You should be able to then install it as a new theme.
If you have any questions or trouble, let me know.
Thanks,
Bill