Dear Felix
On [date] we called your attention to your account balance in the amount of $ [dollar amount].
According to our records, we have not received either a reply to our letter nor a remittance to clear this account. We extended credit to you on your account in good faith and expected payment under our normal thirty-day terms, which we feel are most reasonable.
So that no further action on our part will be necessary, we shall expect a remittance by return mail or the courtesy of a reply to our letter as to why payment is being withheld.
By: Lydia