Contact the merchant in writing, and provide the date (or dates) on which you instructed the merchant to cancel the service. In the letter, provide information on how you cancelled the service or provide a copy of the notice. Tell the merchant to cancel both the service and the charges to your account. You should maintain a copy of this letter for your records.
You should also notify your credit union that you no longer authorize these charges. If you are asserting that the charges already debited were not authorized, and the merchant did not issue credit for those charges, the credit union may request that you complete an affidavit. The credit union will investigate your claim.
You can ask your credit union to place a stop payment on a preauthorized transaction. To stop payment, you need to notify your credit union at least three business days before the transaction is scheduled to be made. The notice to stop the transaction may be made orally or in writing. A credit union can require written confirmation of an oral stop payment request. If the written confirmation is not received within 14 days of the oral notice, the oral stop payment order ceases to be effective.