In business transactions, there might be times when a problem arises that cannot be easily resolved by phone calls. Problems could arise from the quality of goods received, late deliveries, poor service, late payment penalty, or not completing a task in the required time frame. You need to put your concerns in writing.
Review the purchase order and agreement for the terms that are in question about goods or services you are dissatisfied with. If you have already made phone calls, send a letter outlining your problems and what the vendor said in response.
Write a letter to the vendor outlining your concerns. Keep copies of all letters you send to the vendor. After each contact, send the vendor a confirming email outlining the issues that were addressed satisfactorily and any outstanding issues. This can be a short note but keep it respectful and professional.
If you have not received complete satisfaction, you need to codify your complaints in a more formal dissatisfaction letter to a vendor. The important items to include in the letter are: terms of the agreement, delivery or performance dates, problems encountered, and copies of the emails you have sent concerning the issues.
While a lawsuit is always possible to resolve a problem with a vendor, this should be the last resort. Lawsuits are expensive and time consuming. If a lawsuit is absolutely necessary, the vendor complaint letters will be a big asset to your case.