Have you ever signed a contract, slept on it and then woke up the next day regretting your decision? Many people don't realize that they can void almost any contract within 3 days of signing for any reason (usually excluding automobile sales). This is called a statutory contract cancellation. It gives consumers a reasonable time to change their mind about just about any contract they sign with businesses and individuals. You can basically consider the agreement null and void as long as you write a letter to void the contract.
Find out the full name and address of the person who you need to void the contract with. If it is a business, get the full business name as listed with the state or on the contract and also add the name of the representative you worked with at the top of the letter.
Date the letter to make it clear that you have voided the contract within the allotted time (usually 3 business days, depending on your state).
Write the customer or contract number related to the contract as a reference at the top of the letter. Explain in clear language that you are canceling the contract with their company. Describe the services that you contracted for in detail. Cite your state's law regarding your ability to cancel a contract within 3 days if you feel the other party will try to give you trouble. You don't need to state why in most cases, but you can if you feel it will make things clearer for the other party. Write your name and address (city and state at the least) so that the other party can identify you easily.
Have the letter notarized at your local bank (many have free notary publics). Get a clear copy of the completed letter with your signature and keep that for your own records. Have the original letter postmarked and get a certificate of mailing from your post office (costs about a dollar). If you want added protection, have the letter certified with a return receipt.