What do I do if a pet owner won’t respond to me?

A client I’ve sat for before contacted me a month ago, asking if I would watch their pet again. I said I was available. He contacted me a week ago asking if I was still available and I said I was. Today is the day I’m supposed to be watching their dog, but neither owner will respond. I’ve contacted them on rover, and at their personal phone numbers, and I’ve heard nothing back. I’ve never been in this situation, so I really don’t know how to handle it.