Write directly to the vendor/merchant to request no further debits to your share draft account. You should provide the credit union with a copy of the letter and inform the credit union that these charges are no longer authorized. Keep a copy of the letter for your records.
You can contact your credit union and place a stop payment order on the transaction. Generally, you may issue a stop payment order for one transaction or place a permanent stop payment order against a vendor/merchant.
To stop payment, you will need to notify your credit union at least three business days before the transaction is scheduled to be made. Notice may be made orally or in writing. However, if the notice is made orally, the credit union may require you to follow up with written notice within 14 days. If you don't provide written verification of the oral notice when required, the oral stop payment order ceases to be effective.