There are a few ways to tell if someone has blocked you from their WiFi network. If you can no longer connect to the network, or if your connection is unstable, that may be a sign that you've been blocked. You can also try looking for the network on your list of available networks - if it doesn't show up, that's another indication that you've been blocked. Finally, if you're able to connect to other WiFi networks but not the one in question, it's likely that you've been blocked.