I changed the resource name, but the resource name has not been updated on Usage and Billing page.

Even if you change the resource name (instance name etc.), that is not reflected in Usage and Billing page. Therefore, when checking Usage and Billing page of the resource after changing the resource name, please confirm the price of the target resource with the ID of each resource as the key.
The ID of each resource can be obtained via portal or API.

Reference: How to check the fixed usage fee
Tutorials - Use NTT Com Business Portal (Business Portal) - Verifying your Contract Information