Unknown devices connecting to Gateway Modem

I am very upset. I had 15+ devices connect to my Gateway modem at 3am and they keep on coming. I cannot connect any of my devices to my network due to these unknown devices piping up in my connection in the Xfinity App. I went to the store and got a new modem and they changed my IP address, but that did not stop the devices piping up in my network. What do I do? I need help!