What does this "unrefundable amount for this month" mean in the bill...

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件名	What does this "unrefundable amount for this month" mean in the billing statement section?
回答	It indicates there is a refund due to double payments or other reasons. We put down the amount for refund on the statement.
カテゴリ	よくあるご質問 > FAQ for foreigners > FAQ English
関連FAQ	By changing the billing origin to NTT FINANCE, is my personal information going to be given to NTT FINANCE? While using "Denwa Bango Hokan" (Service to have NTT docomo keep your phone number for up to three years and reactivating it again after you come back to Japan.), can I apply for "Omatome Seikyu Service (combined billing method)"? I'm using online billing service (@Billing, My Billing, OCN my page, My docomo) of each communications company. Can I still use these websites after applying for "Omatome Seikyu Service (combined billing method)"?