Block Hackers Getting Into My Network

4.7.21 - Good afternoon. I want to know HOW to BLOCK hackers from getting into my network? Since 3.14.21 when they took it down by modifying McAfee drivers [yes, it was horrible], I've renamed the router, changed its PW and the WI-Fi PW at least 3 times. When I see them in xFi by the system telling me I have 'new devices' that don't belong to me, all I can do is to [a] pause them, [b] refresh my screen, then [c] go back and 'forget them.' Unfortunately, that only helps for a while.

When the major hack happened, I got rid of the McAfee and got Norton 360. I let their techs AND Xfinity techs both get on my system to see if they could fix everything. The Norton folks were great, and we found on the Xfinity router website that there was a device that was offline. So, my question became how could I take them out? In other words, they weren't showing on the xFi app or connecting via the website, but showing on the router's website [you know, 10.0.0.1]. I also asked how can I block the extra IP addresses, as I will only have a given number of devices to connect. I figured all the rest can be blocked, and that would also keep anyone out unless I granted access.

When I called back, Xfinity tech support told me that I couldn't take him out. All I could do is what I already did, or add them to a parental thing and limit their access. Don't use the parental thing, I don't need it. They also said I could not block my extra 200+ IP addresses that the router possesses. That was the stupidest response I've ever heard, after many years of sourcing and building networks myself. I've seen it done, but I guess I was in control of the server at the time... Maybe not so much when the server belongs to someone else. Today, I was online w/two devices. About 10, 15 mins. later, xFi told me there were NO devices connected even tho I was still online. I did a reset and so far, it's alright. But why would it say that in the first place? 

So, Community - is there someone out there who knows how to correct these matters? I'll be changing the router name and PW as soon as my class is over later today. But when I walk away, I disconnect the router, period until I sit back down. It's crazy. Thanks in advance for your assistance.

Ms. J. S. Butler