Use this language on your own company letterhead.
On [date], we received your check #[check number] in the amount of $[amount]. Your check was dated [date of check] and was drawn on the [name of bank]. The account was in the name of [name on account holder]. Your bank returned the check to us due to insufficient funds (or because the account was closed). You must make payment to us immediately to avoid legal action. Please visit us in person to tender a cash payment. You may also pay by a cashier’s check, certified check, or credit card. If you do not pay us within five days, we may take legal action, seek criminal prosecution, assign your account to a collection agency, and/or report the debt to a credit reporting agency. If we file suit, we may seek additional damages pursuant to state law, as well as our costs and legal fees. We expect your prompt attention to this matter.