My thinking about the sketches were keeping the bill in one page and how it would fold to be a mailer. I also made some sketches on the pattern and how to keep the branding style.

This is the unfolded view of the outside. For easy access to what the client is looking for, the amount that the client has to pay comes in a bigger font. The middle section is part of the self-mailer part of the bill and the far right is the face of the bill that keeps the branding colors of the company.

This is the unfolded view of the inside of the bill. Although the statement says it's from the last 12 months, this is how it would look like if the client hasn't been with the company for at least twelve months. The middle section shows the lines in the account and the current amount to pay for each line. The far right shows the clients name, account and a QR code for those who prefer to pay with their phones.

Having the bill being a self-mailer saves paper when printing and saves storage space for clients that like to keep their bills for further documentation.