If you are going to mail a check which needs to be applied a certain way to certain invoices, ask whether you can mail the check to this particular person to make sure the payment is applied the way you've both agreed that it should be applied. Have all the information needed to solve a problem at hand before you contact a customer service representative, whether by phone or mail. Provide all relevant information accurately in written correspondence. When using written correspondence, be sure you send your letter to the correct address. For example, do not send correspondence concerning a problem to the vendor's payment receipt address.
Carbon copy all interested parties within the vendor's organization.
Keep copies of all correspondence regarding a problem, including e-mail messages and your notes of telephone conversations. Until the problem is finally resolved, keep all relevant documents in a file close at hand. Don't file them in your general file for that publisher. This way, if you receive a phone call from the vendor, you will be able to quickly discuss the matter. Also, because the file is within your view on a daily basis, you won't forget that the problem is still unresolved.