Dear Sirs,

Account No.****
As you are usually very prompt in settling your accounts, we wonder whether there is any special reason why we have not received payment of the above account, already a month overdue.
We think you may not have received the statement of account we sent you on **** showing the balance of $**** you owe. We sned you a copy and hope it may have your earl attention.

Yours faithfully,
***