When a customer complains, thank the Lord. You may get a chance to fix it.
What they are telling you is “I am your customer, and this hurts.”
Regardless of whether they are “right” or they are “wrong”. Regardless of the rules, or the logic, or the systems. To them…It. still. hurts.
They are telling you, “I am frustrated with the rules and the systems, but you get a chance to fix it before I take my business elsewhere.” A customer complaint is an act of caring. Most of the time they don’t complain and the business is gone. We get the message too late.
Break the rule. Break the system, if you can. If you can’t, make them feel validated, apologize and make it as painless as possible.
Most of all, make sure you understand it from the customers point of view. They are never wrong about how they feel.