Common reasons are as follows:

• A campaign is being applied

Your monthly charge may be free for the respective month depending on the campaign or reward which is applied to your subscribed service.
Please check your billing statement on My Page.
Check the Billing Amount/Statement

• The billing is delayed due to the closing date of your registered payment method

Usage charges for Asahi Net are closed at the end of every month, and they will be billed in the following month of the usage month.
Depending on the payment method, you might have to wait between one and three months after your usage month until you can check your billing statement.

• You may be using a service which is not billed by Asahi Net

You will not be billed by Asahi Net depending on your subscribing service and/or payment method.
Asahi Net docomo Hikari: Your ISP charge is billed by NTT docomo.
Asahi Net All Apartments Plan: Apartment residents will not be billed for their ISP charge.
Any Asahi Net optional services: Those charges are billed by Asahi Net.

If your registered payment method is Billing by NTT, you will not be billed by Asahi Net.
Please check the billing statement from NTT.