Neighbors devices connecting to my network

Over the last week or so I've been getting notifications saying new devices are connecting to my network, like phones/macbooks/firesticks/etc. I live in an apartment complex but I don't know any of my neighbors and I've never shared the password with any of them. I would say my password is pretty secure and can't be easily guessed, so how are people accessing my wifi? How can I prevent this from happening? I've read other threads and the solution seems to usually be to disable the MoCa filter (which I could be totally misunderstanding, I have no clue how any of that works, please correct me if I'm wrong) by going to a link labeled http://10.0.0.1  and logging in with the name "admin" and password "password," it won't let me continue. I'd really like to keep strangers from using my internet, and I'm mostly concerned about how they might be doing that if it's already password protected. Thanks!