If there are two surveys being sent out in the same email to the customer, then you have inserted the Satisfaction survey placeholder in the email notification. Also, you have set it to be sent when a ticket is Resolved or Closed under Admin > Customer Satisfaction.
Therefore, check if there are any custom email notifications being sent out using an Observer rule from Admin > Observer. Also, check if the placeholder is present in the default email notifications under Admin > Email notifications > Requester notifications.