Hi Joohyok,
Thanks for being part of the AGL Community.
We would need to check your account to confirm this, however it may be due to the usage on the APP not updating until 24-48 hours, or you may be looking at the usage costs only which don't reflect the other bill charges, such as supply charges. So that we can determine the exact cause for this, please get in touch with us here.
Kind Regards,
Jenna