Had a customer ticket after hours claiming that his web hosting was down. We went in to check and found out that his domain expired. Invoices was emailed to him and also posted to him much earlier.
He admitted that he overlooked the invoice but insisted that it was our error as we shut down the domain at 2pm instead of 2359pm. But we pointed out to him actually we never shut him down his domain expired and that why it was down. He continued putting the blame on us. We told him we have no control over when the domain registrar shut down his domain name since it expired. He insisted that we were in the wrong and said that expiry was that day so he had just post his cheque and therefore had paid for it. Posting a cheque is no proof of delivery or receipt, it takes a few days to receive!
One of our tech had no choice but to pay for him with his own money to renew the domain, he send about 15 emails blaming us on every single detail of the invoice that he claimed misleading. That was a real unreasonable customer.