Hi,
This does sound like quite the problem. Couple of things.
The Samsung Note 4 is 5 years old now, so it is not being supported officially by either Samsung or Google.
When the “Downloading” screen comes on, it means that it’s looking for the Android OS. It could be that the previous person reset it incorrectly, hence when it was turned on for the first time, after the reset, the system became stuck in a loop. The little tip off, is when you see the little Droid robot on it’s back, with the chest opened and a red symbol hovering over it.
You can try to download the original ROM and install it on the phone, but it can be challenging if you’ve never done it and you need a computer. If you need help with this and want to try it, I can assist you.
My best recommendation, and I know you won’t like it: Get another phone. And try to get a newer device. Lowest model I’d go if you really want one from the Note series, get a Note 5. If this is not a deal breaker, then you have an open field of devices.
Hope it goes well.
Alex H.