samsung c71kw-400 will not connect to wi-fi
I have new ATT fiber optic service with a BGW320-500 modem and DirectTV Streaming service. The Samsung C71-KW-400 DVR boxes I received with the package to access DirecTV Streaming via Wi-Fi will not access the internet via wi-fi. Every other device in my house (iphones, laptops, Amazon Echo, etc.) have no problem accessing the internet via wi-fi. It's only the Samsung DVR boxes cannot access the internet via wi-fi. If I use ethernet connection, the boxes do access internet, but I have 3 boxes and I don't have ethernet connections for all of them. In the setup for the box, I see my wi-fi SSID. If I select that and I enter my wi-fi password, I get the message "Can't Connect to [SSID Name]". I have tried rebooting everything (the Gateway/modem, my third TP-Link Deco mesh network and the DVR boxes), but nothing works. I called the ATT Tech Support line, which was worthless. They knew even less about this setup than I do. The first person told me to reboot everything (duh), same with the second level person. The third level person (after they asked me to re-explain everything) said they do not support this equipment any longer. I've had the equipment for less than 2 weeks!
When the service was initially hooked up, the DVR boxes worked (accessed wi-fi). But, because I had both the Gateway and the TP-Link Deco mesh network serving as routers, my understand was that I could potentially have a problem with "double NAT". I'm not an expert on home network issues, but I was concerned this would cause a problem. So I've tried configuring the Gateway as the router and my mesh network as Wireless Access Points, but that started the problem with the DVR boxes not accessing wi-fi. So I tried configuring the Gateway in "pass through" mode and have my mesh network serve as router, but I still had the problem with the DVR boxes not accessing wi-fi (I can select the proper SSID and enter the password, but I get the "Can't Connect to..." message.
I've tried using the factory reset button on all the equipment to go back to where I started, but that doesn't work either.
Someone please help! I just want to be able to watch friggin' TV on this supposedly wonderful new system I have! Spectrum cable internet was slower, but it certainly wasn't this much trouble to watch TV!