Уважаемые знатоки, подскажите, пожалуйста, нижестоящая фраза правильна?
Dear bla,
it looks like the attached invoice still hasn't been paid. Could you please check this and come back to us?
Не слишком ли "вольготно" звучит? Как бы это ещё вежливо сформулировать?

как вариант:
We cannot determine that the attached invoice has been paid. Could you please check this and come back to us?

Спасибо!
We cannot determine - это не слишком официозно звучит?
У меня шпагат между официальным напоминанием и дружелюбным вопросом...

Тогда может - we do not see the payment...?

According to our records, your account is overdue (e.g. 5) days. Please check the payment status for our invoice No. and advise us as soon as possible. Should you have paid the invoice in the meantime, please ignore this reminder. If you settled the invoice by the due date, please excuse our mistake.

Ба!!! Вот это стиль! Спасибо!