123 Main St.
Re: Your account balance of $[_________]
To XYZ Company:
Your account balance shown above has been outstanding since ____________ and remains unpaid.
[Alternatively: We have not received payment of our invoice #[___], dated [____________], 2015, in the amount of $[____]. As you know, under our terms, payment of the above invoice was due on __________________.]
We have sent you statements of your account for the last _____months, but have received no response or payment.
[Optional: If you would like to discuss your account, please contact us without delay.] If your account is not paid in full within ____ days from the date of this letter, we will have no choice but to refer this matter to counsel for appropriate legal action.
c: [Insert name of firm]