Austin Parker,
1234, West 67 Street,
Carlisle, MA 01741,
(123)-456 7890
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear Austin Parker,
We apologize for the billing statement sent to you twice this month. Kindly ignore the second bill you received . Our I.T. team has already established a software, meant to track all correspondences, emails, and mails (including billing statements) sent to the customer. Nonetheless, we sincerely thank you for alerting us, and for helping us keep transactions systematic. We always look forward to serving you.
Sincerely,
Primel