If you rely only on customer satisfaction survey scores, you might be missing out valuable feedback that customers never give you in the surveys. You get feedback at all times from customers, sometimes direct and sometimes indirect. How you react to it defines how customers perceive your service as. If you don't listen to your customers during regular interactions, they are less likely to give you any feedback in customer surveys. They are more likely to stop giving you feedback. Worst, they will tell others about the bad service instead of telling you about it.
I am sure we work very hard to exceed customer expectations. But let's face is, as service providers (internal or external), sometimes we do get irritated at customers. We believe so much in our own service levels that we forget to see if these are still relevant for the customers. How we react to the inputs when a customer does give us some feedback changes the way we will receive feedback in the future. Sometimes inadvertently while responding to a customer feedback, we may put them off by disbelieving their feedback by telling them the unlikeliness of a service failure because of robust processes and systems. Instead of lauding internal processes, all that is really needed is to acknowledge the experience customer might have had.
So when you receive any feedback from your customers, first respond with a simple acknowledgement and apology of the experience. This is usually enough to turn the customer around. Later when you review the situation and identify the cause of customer experience, you can get back the customer with more details. This could even include things where the customer may have been at fault and things that you want the customer to change.