Dear Elena, good morning! Yes, of course, we have worked with your company for a long time and we trust you concerning payment of your accounts. However, the management of our company insists on payment of invoices strictly according to the terms stipulated by the contract. It is necessary for us to do this so we can decrease the growth of our receivables. According to information available to me, the payment terms under the contract are that payment is due within 30 banking days after receipt of invoice. We sent you invoices for July flights on 05.08.2012, so your payment was due on 17.09.2012. It is only for this reason that we requested a letter of guarantee from you. Please let me know if my data is in error; if so, I will resolve the matter with my management.