Samsung s7 severe WiFi problems?

I just bought a 700 dollar Galaxy s7 after 2 years of enjoying the s5, and i'm having major issues with the Wifi. The phone connects just fine and everything works for approx 5 seconds. After that the phone will stay connected to the router, but the download and upload speed will fall to 0. Resetting the router and modem didn't work. Resetting the phone didn't work. Deleting the router and reconnecting didn't work. Factory resetting the phone didn't work. Trading in the phone for another s7 didn't work. Nothing seams to be working. I have many many devices that work off the router flawlessly, among which include 6 game consoles, 4 phones, Ipod touch, 3 Laptops, Smart T.V., Amazon Fire Stick, and countless visitors' phones. And no, this is obviously not all at the same time. Currently I have nothing connected to the router besides a laptop and the s7 and still nothing.

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