We must insist upon a prompt settlement
We must, therefore, insist on the terms of the agreement
We note that the time is at hand
We offer you the services of an expert
We particularly want to interest you
We realize that this matter has escaped your attention
We realize that this is simply an oversight on your part
We regret exceedingly that you have been inconvenienced
We regret our inability to meet your wishes
We regret that owing to the press of business