Cannot Reduce iCloud Mail Storage

My iPad and iPhone use the same iCloud account for backup. Under iOS system preferences > iCloud > Manage Storage it said my mail was taking up around 2 GB and then I did the following:

1. Deleted all messages in Inbox, Sent, Archives, Deleted Messages, and every other folder I have. I literally have 0 messages in every folder.

2. I have restarted all my iOS devices.

3. When I went back to iOS system preferences > iCloud > Manage Storage it says my mail is NOW taking up 4 GB.

I have logged in to iCloud.com and there is nothing in my mail folders. Any thoughts?