Good morning @Junipher!
Being able to check usage on your myAT&T account is a great feature. I would be delighted to help out and point you in the direction so you can view your usage again!
This awesome link takes you right to your myAT&T usage. You should see a drop down which states View Usage by. Select the drop down bar and it should allow you to view your usage by Data, Talk and Text. You can also select usage by billing period.
I hope this helps out! Thank you and have a great day!
Portia, AT&T Community Specialist