View the list of Sample Business Letters Refusal to Extend Time on Payment of Invoice Disclaimer: Be aware that some of these sample letters have legal, financial, or other implications. If you are not sure about the use of any letter, consult with an appropriate professional first. Refusal to Extend Time on Payment of Invoice Dear We regret to inform you that we are unable to extend any more time for payment of the above invoice. We feel that we have been extremely patient, but if we do not receive payment in full on or before (date), we shall have no other choice but to turn this matter over to our attorney with instructions to use all available legal remedies to collect the amount owing.