The stats on the workspace setting page do not update in real time. Give it several hours to a day or so.
Also, attachments that are deleted within your snapshot history can also still count against your attachment space. (If you restore a snapshot, the attachments are restored.) So, it might take up to two weeks to regain the attachment space.

Thank you!

Hi! Where can I find the workspace setting page? I can't seem to find it. Thank you.

Go to your Account page (https://airtable.com/account) then in the sidebar click on the workspace under the Workspace Settings list.

Yesterday was when I finally got around to addressing my attachment limit situation. My attachments were at 1.9GB, almost double the limit. I downloaded the largest ones for safekeeping and deleted them from my base. @kuovonne's comment above indicated it could take up to two weeks for the count to reset, but today it was updated when I checked, less than 24 hours later. What a relief.

For anyone wondering how to find the largest attachments, I went with the low-tech solution mentioned in this community comment about viewing file size. I created a new view that was grouped (and hid all the other fields except for attachments, for less distraction), which shows the total size on a given record as well as a total on all records in that table at the bottom of the screen. It doesn't identify individual files, but helped figure out where the worst offenders lived.