Nowadays, folks don't answer their phone, listen to voicemails, or check their mailbox for days. Email is probably the best chance you have to communicate with them.
^ This. I don't check mail for days which drives my wife crazy. It's all junk except for the occasional card, jury summons, or the IRS having a disagreement with me. There's an elderly couple a few houses up from us in Nags Head. They are long since retired and come to the beach for many weeks on end throughout the off season. On multiple occasions they had to return home to pay bills!
I felt like throwing them a bone about setting up online banking and electronic everything then they could just stay at the beach vs. driving back to Boston, but they're up there and I doubt would take to the new way.