@Kara329 Did you communicate your expected arrival time to your host? Or just show up and expect someone to be waiting? How are you trying to contact them? Phone, text, Airbnb message? Maybe try a different method than what you are using. If you still can't get an answer, you can ask Airbnb to try to contact the host.
@Kara329 Try sending them an Airbnb message. Unless this was a last-minute booking, only 3 hours notice of your arrival time is not very respectful, unless you had already set up that arrangement with the host so that they would be expecting your call the morning of check-in. Most hosts would like that information a day or so ahead, so they can plan their day.
@Kara329 When is the last time you communicated w/the host about checking in? Is it self check in or something else? If you can't reach the host by the official check in time you will have to contact airbnb and they will probably try to reach the host and if they can't will help you find a new place and cancel w/out any cost to you