Illegal connections to my WiFi

Hello

I have discovered illegal connections from people outside my home, that manage to connect to my Wifi. Xfinity lets you see in your account, the connections made and date, then you see HOSTNAME, BRAND, IP, MAC etc

I do not have an iphone, I do not have a laptop I have the info from these devices. This explains why my devices get HOT because these "evil outsiders" are litterally stealing my WiFi and making usage higher. How do I get Xfinity to understand this and secure my WiFi, last time I called their dept that deals with cyber security they tried to assure me all was well. So I took their word for it and let it rest.

But I got ALL THIS INFO of at least 3 iphones and another computer that connected to my WiFi in February. and someone is consistently attacking my indoor security cameras like crazy and all Xfinity does is say "restart device" to clear the threat.

Do any other users have better solutions, other than turning my cameras off which is not an option for me, as to how to secure my WiFi to stop "people from outsode my home, no doubt neighbors too lazy to pay for their own internert and losers" from draining my personal bandwidth, causing my devices to get extremely hot and draining down my speed. And solutions about securing my indoor cameras because Xfinity doesn't seem to care!