When attempting to collect an overdue balance from a client who has not made payment, it is crucial to approach the situation professionally, assertively, and within the boundaries of the law. 

Here is a recommended method for collecting an overdue balance:

1. Send a polite reminder: Start by sending a friendly and professional reminder to the client, stating that their payment is overdue. Include specific details about the outstanding balance, the due date, and any applicable late fees or interest charges. Request immediate payment and provide clear instructions on how they can make the payment.

2. Follow up with a phone call: If the client does not respond to the initial reminder, follow up with a phone call. Be polite but firm, and emphasize the importance of resolving the outstanding balance. Inquire about any potential issues or concerns that might be hindering payment and try to find a mutually beneficial solution.

3. Send a formal demand letter: If the initial reminder and phone call do not result in payment, escalate the matter by sending a formal demand letter. The letter should outline the outstanding balance, the consequences of non-payment, and a deadline for payment to avoid further action. Make it clear that you are prepared to take appropriate legal steps if the debt remains unpaid.

4. Offer a settlement or payment arrangement: In some cases, clients may be experiencing financial difficulties that prevent them from paying the full amount. Consider offering a settlement or proposing a structured payment arrangement that allows them to clear the debt over time. Ensure the terms of the agreement are reasonable, feasible, and legally sound.

5. Engage a collection agency or attorney: If the client still fails to make payment or negotiate a resolution, consider engaging a professional collection agency or an attorney specializing in debt collection. These professionals have expertise in handling difficult cases and can pursue more aggressive collection actions if necessary, such as filing a lawsuit.

6. Preserve records and document communication: Throughout the collection process, maintain detailed records of all communication, including dates, times, and the content of conversations or correspondence. This documentation can be valuable in case legal action becomes necessary.

Remember to adhere to relevant laws and regulations, such as the Fair Debt Collection Practices Act (FDCPA) in the United States, and to act ethically and professionally throughout the collection process. It is advisable to consult with legal professionals who specialize in debt collection to ensure compliance and obtain guidance specific to your jurisdiction.