Two things to check/do:
Find all data associated with the account and ensure it is permanently deleted. This is how: https://wiki.galaxyproject.org/Learn/ManagingDatasets#Delete_vs_Delete_Permanently
Go into the Admin section of the UI, click on User Management: Users, search for your account, and use the pull-down menu to recalculate disc usage.
If neither of these work, there are other configuration setting that could be a factor. Please let us know more about your local, the version of Galaxy running, the source if not from github (http://getgalaxy.org), and we can provide more help.
Thanks, Jen, Galaxy team