consolidate billing

Have you added all the linked accounts to the CB?

AWS Organizations provides consolidated billing so that you can track the combined costs of all the member accounts in your organization. Therefore, you should be able to combine all the costs from different accounts using that feature

Could it be that you added your account to Organization (or joined Organization) somewhere in the middle of the month, but before doing that, you accrued charges on your linked account for the first part of the month when the account was still standalone? In such case, your linked account would still get invoiced for the days/hours of the month when it was not part of Organization. All the charges for usage that happened before joining Organization are still billed to your linked account. There may be a way for a Payer to pay for your charges for that month for the days before you joined Organization, so I would suggest reaching out to support. The support case need to be opened on the Payer account if they want to cover your charges for the first part of the month (before you joined Organization).