Première relance pour impayé (Lettre-type en anglais)

Dear [Mr or Mrs or Sirs], Checking our records, we have noticed that invoice [références] for [montant] due on [date] has not yet been paid. We trust that this is a forgetting on your part, but must ask you to be kind enough to give this matter your immediate attention. If payment has already been made, kindly disregard this notice. Should you wish to have any further information about your account, please do not hesitate to contact us. Yours sincerely [votre nom] [votre fonction]