Before starting a claim it is normal to write to the debtor one last time.
Most businesses will make this letter the last part of their normal credit control process.
This letter may be useful as evidence if you have to take legal action. A copy of it will be useful to show that you have attempted to resolve the dispute before going to court. It also serves to show that they were warned that legal action would follow if they failed to pay.
This letter is usually referred to as a 'letter before action'.
A 'letter before action' should usually be fairly short and to the point. The letter should state:
Your name and address will probably be on your stationery. If, for whatever reason, the payment name or the payment address is different state this clearly in the letter.
There are a few other things you might put into this letter. You might mention that previous reminder letters, invoices, copy invoices or statements have been sent or ignored. You might include copies of the outstanding invoice(s). This will at least prevent the debtor from using the excuse that they have lost an invoice.
It is probably a good idea to insist that if they want to dispute the invoice that they should do so in writing.
Example letter in: