Hey @lithajo48!
This is a great question about checking the usage on your myAT&T account. I would be happy to get you pointed in the right direction!
You are completely correct; there is a way to check all usage for any line on your account. Calls, text, and data amount usage can all be tracked by clicking here and then logging into your myAT&T account.
For other options in checking out usage since the last bill, please check out this great article which details Star Services, and how to view additional bill cycles. I hope this helps!
Have a wonderful day!
Fiona, AT&T Community Specialist