Windows 10: Network Intruders

So I have / had network intruders. I thought it was computer-based then noticed weird stuff on every device. I tried changing the network password resetting all the devices, the modem is Fidium so you can’t really access it once I connected them back to the network, they somehow got back in so now I have a new Internet service provider. now my question is should I reset all of my computers again before connecting to the new network? I know it sounds like common sense, but Xfinity was pretty clear about how secure they are, but I know if anything is secretly installed on my computers or any

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Phone intruding on Windows 10 home network

Almost daily when I look at "Network" in file explorer I see an unknown phone listed as "Phone" with the name "cingular_us". Using properties I can lift the MAC address of the phone, and I have of course denied it wireless access to my network. I have also
set up device trust under Firewall in Norton Internet Security. Nothing seems to keep this device out.

Anyone else seen this? To me this seems like a pretty bad problem, and at this stage I am not sure how to get to the bottom of it and how to keep intruders out. Any suggestions?

 

Phone intruding on Windows 10 home network

Thank you for your response, ThofikhAhamad.

I did both of the items that you suggested, and still "cingular_us" showed up under Network.

I started seeing the issue while still running Windows 8.1. At the time I did not think much of it. I then upgraded to Windows 10, and since I am seeing the intruder more often, it has started to worry me. Should I be worried?

 

Did our Epson printer get hacked?

Another question, is this on a home network or a work network? The steps @eidairaman1 listed are always a good first step. If this is on a work network you manage, I'd be much more concerned than the home one. It is possible someone is screwing with you, but malware could also be the culprit.