R6300 v2: Updating FIrmware

I've just gotten off the phone with a Netgear tech support agent. He got to the root of the problem and I'm going to follow his suggestions.

The router was bought on Amazon, and it's a refurbished model. Apparently the vendor, "flaknet," is not an authorized direct vendor for Netgear products, and used Amazon as a platform to resell a used router. The router was almost certainly provided by Charter/Spectrum, and they altered the firmware for the router, which is why none of the files available on Netgear are recognized as correct. It's also why the Netgear Genie keeps saying, "firmware invalid" when I used it to try and automatically install an update-- it's not saying that the firmware update is invalid, it's saying that the EXISTING firmware already on my router, is invalid.

Spectrum will undoubtedly keep screaming in protest that only Netgear can fix the problem, when in fact they cannot, because the firmware was altered by Spectrum (Charter), which they will refuse to acknowledge responsibility for. 

So... the solution?

Just continue using the router normally. The agent strongly believes that, outdated as the firmware is, it doesn't pose a serious security risk to my network. Indeed, I never would have known that the firmware was outdated except for my Avast Antivirus (free version) giving me a popup when it detected the router being hooked up. I just need to click off whenever there's a popup. The reason I bought the router is so that I can have internet connections for both my Roku-compatible TV and my desktop computer at the same time. And I also have WiFi now if I ever would like to use it.

So, my apologies for the over-wordiness, but apparently, even though the problem cannot be fixed short of returning the router and getting a different one... apparently I don't need to. I can continue using this one as I have been since I got it two days ago.

My thanks to antinode and plemans, so much, for the help they provided. I'm going to mark this solved.