Excellent suggestions here. When talking to your customer (as said, do it in person!), use this technique called "forbidden to solve". When you talk to your customer, ask only open questions... questions that you cannot answer with yes or no. Summarize a lot, to get a clear understanding. This will not only make you an active listener, but the customer also gets the feeling that you listen to him/her.
Then, when you have a clear understanding of the problem: fix it! FAST!
One of my most patronised customer is threatening to leave me because of a bad experience they had with my company.
Lesson to learn: it takes only one(!) bad experience. Make sure that you have the customer service culture, customer focus, and customer service rep empowerment to solve issues as they arise.