How to win back customers and regain customer trust

What this question really emphasizes is how important it is to make sure that we do it right the first time, because once we lose a customer, as is clearly the case here, we may never get a chance to be able to talk to that customer again. We know that, so what do we do now?

What is not clear from the question is whether this is a business-to-business (B2B) or business-to-customer (B2C)...

setting. If it is a B2C setting then it's going to be very hard to go to a particular customer and make everything alright. If it's a B2B setting, then it's worth investing some effort into going back to the customer and educating him about the new things we have, making it clear what we can offer him now and also emphasizing what's in it for him by at least reconsidering doing business with us. In the meantime, what we want to do is make sure that we are doing everything as well as we can and hope that word of mouth will reach that customer and he might give us another try.