Try logging out then back in again to recalculate the quota. Also, double check that the data was actually purged (permanently deleted). Just "deleting" does not remove the data from the account quota.
- The account usage quota seems incorrect https://galaxyproject.org/support/account-quotas/
- Checking for active vs deleted vs permanently deleted (purged) datasets and histories https://galaxyproject.org/learn/managing-datasets/#delete-vs-delete-permanently
If that doesn't reset quota correctly, are you working at Galaxy Main https://usegalaxy.org? Or if working somewhere else, please describe where (URL, if public).
Thanks! Jen, Galaxy team