Netgear C7800 Dual Band Issues

I have a Netgear C7800 that I bought about a tad bit over a year ago. Long story short, the dual-band modem router has had a major issue sometime mid lifetime of ownership. The 2.4GHz connection can be broadcasted but FAILS at giving off an internet connection to any device that connects to it. No matter what device I try with, no internet, however; the 5GHz conncetion works totally fine and I am able to do what I would normally do with it. Although the 5GHz connection works and the 2.4GHz DOES NOT WORK, any and all older devices that are unable to connect to the new 5GHz are now internet-less. Now for the main question(s) I am here to ask:
1) Why is this happening?
2) How can I resolve this issue?
3) Is my product now single-band for its remainder of life?

Little more info…
Now to get rid of the common comments and things that I could do/should have done. Yes I have talked with my ISP multiple times over multiple phone calls lasting over sixty minutes each and getting nothing but "talk to Netgear". Yes I have talked to Netgear about the dilemma and they have told me on a few phone calls to "talk to your ISP, it's their problem, not our product". Yes I have researched and have done probably a little of everything from as simple as turn off and then back on, unplug, wait "ten" seconds and plug back in, factory reset, firmware update is impossible to do, unless pushed via my ISP and my ISP alone. I have no power in being able to downgrade to a previous version where it once worked. ISP is incapable of downgrading my firmware since all firmware updates are pushed via ISP and can not be reverted back. I have also searched through the community forums here and have found "solutions" to other people's questions about their troublesome product within the same issue on my product and those solutions do not give me any positive results. 

…not so little info I suppose

So, for any single person who has a single clue as to why this is happening and how to resolve it, I am all ears and hopefull you can salvage this piece of plastic to give the old plastic some internet. Even though small possible solutions like mentioned have been done, I will attempt again, but I recommend to not make waste of your time if that is what you offer to me as a possibility. I feel like everything has been attempted and no luck. I thank you ahead of time for anyone who knows how to get to the bottom of this and get it up and working like new. I also thank the people in advance to offering possiblities on solutions or any aid in my quest to get a fix for this modem router.

Thank you again and may we once again allow these old devices to see the internet once more.
Thank you

***Rant, Unneccasry Read(but goes out to you customer service managment who cares about this)***
All products I have ever owned by Netgear have been a collasal let down from being given to me to being purchased. The Netgear "specialist" support is another let down due to my previous year having spent little days out of it to try and get a fix yet failing each attempt with no help other than mentioned "call your ISP. Their fault not ours. We have your money. Don't care. Thanks." (I jest in the last few out of this small enraging convenience I have built up for quite some time). In hopes of fixing to sell away and not giving someone the short end of the stick on the product. Never purchasing another Netgear product. Will decline any and all netgear products. ♥☺