@Janet21:
The 3 messages you have sent, were they through airbnb messaging system? Hopefully they were, that way you can contact Airbnb directly and request they contact the guest on your behalf. They will see you are doing all on your end to communicate with the guest.
Sometimes guests are traveling from one country to another and have limited internet access. Hopefully your guest is ok (safe).
I would send a 4th message confirming the time they can check into your listing and specific instructions on how to get in touch with you if they have any questions.
I tried to view your profile but couldn't see your listing. I am not sure what cancellation policy you have an effect but whether they show up or not, the cancellation policy you had in effect at the time they booked will be enforced.