You are paying a big bill for an Internet service to have more speed, but you don't get it. One of the reasons is that, maybe, your neighbours are stealing from you. Ok, you set up a password, but there are ways to bypass it. So what should you do?
To see who is using your Wi-Fi Internet connection there is an app that will show this. You can download it from Google Play. It is called Fing. How can you use it? After you install it, connect your device to the Wi-Fi network you use and you want to test. When you open the app, on the top you will notice the name of the network you are using. Tap on the refresh button and there will appear what devices are connected to your Wi-Fi connection. Fing lets you do a lot of changes and you can get some reports. For example, you can change your IP name, as to know which are the infiltrators.
To block users that you don't want on your Wi-Fi, enter your IP address into the browser on your computer. Then you should introduce the username and pass of your router. After you enter the router's menu, change your password.
If this doesn't work, note your MAC address and after that access the block devices option in the menu. In Access Control, choose your MAC address. This will block other devices that try to connect to your network.
Note! If you have friends around you should uncheck that option as they could connect to your Internet network.