Church,
I'm guessing you had a letter from your bank informing you so - Did they tell you why it bounced ? Depending on the reason, you can approach the customer in different ways - If it was 'Payment countermanded by order of drawer' ie, they stopped it, go round with some muscle and a length of 4x2
If it was any other reason, refer to drawer or refer to drawer please represent, then like Danny said, be lighthearted at first and see how they are - chances are theres a good explanation