Not your problem anymore. I had that happen to me recently. It was a $40 pair of sneakers and the buyer wanted them delivered to her dorm. I asked if she was sure and she said yes. I sent them with delivery conformation. A few days later she e-mails asking about them. I looked it up and they had been delivered the day before. I gave her all the info and never heard from her again. I don't know if she eventually got them or not. You have done all you can.