Answer:
If a neighbor is able to regularly hack into your secured wireless network without your knowledge or permission, it is possible that a security loophole has been left open on your network. One possible loophole could be that you have not changed the default login credentials for your router's administrative interface. The neighbor may have been able to access the router's settings by guessing the default username and password, and from there, they could have changed the Wi-Fi password or other security settings to gain access to your network.
Another possible loophole could be that you are using an outdated or weak encryption protocol for your Wi-Fi network, such as WEP or TKIP, which are known to be vulnerable to attacks. In this case, the neighbor may have used a tool or software to crack the Wi-Fi password and gain access to your network.