The space used is calculated over ALL bases in your team. Could you check if there is another base in your team that occupies quite a bit of storage? As team admin, you can actually do that yourself: Click on the avatar, choose “organization admin” and then navigate to the menu item “Bases”.
Also: Please clean your trash. You can also do that in the “Bases” menu in the organization admin. Just pick the tab “Trash” and then click “Clean” in the menu bar.
If you are using the SeaTable Cloud - The bases are saved in a different server than the interface, therefore when you remove a base or empty the trash, the storage calculation could take 15 minutes or up to 1 hour to update.
So this is really strange. Are you sure you have checked this with all the bases? As even when you have deleted a row with attachments, its attachments are still saved in the base, which can be seen in the attachments management.
There is only one base, and I went through all the folders. There are 56 files, two with 9.8 MB, the others below 1MB. We upgraded to a paid plan for now, but it would be really good to understand what is going on.