I too have tried everything. I also was told by a Heisense tech that I have a software problem. So I return that tv just bought a new one, Same issues.
I literally did all of that and nothing worked (had all 0s -MAC) it was irritating because at times it would work but then do the same thing. The last time It just stopped working. I was never able see anyones wifi nor my hotspot.. I had to get someone to come in to fix my TV. Unfortunate as I bought this in February..
If the Wireless MAC shows all zeros (00:00:00:...), then normally indicates an issue/failure with the wireless adapter inside the TV. Many have found that providing an extra ground wire to the card has resolved the issue. (handy info for your TV repairman or a friend with soldering skills).
If you just purchased in February, should be under warranty from TV manufacturer. (https://community.roku.com/t5/Manufacturer-Support-Warranty-Resources/Contacting-Support-for-Your-Ro...)
If occurs later outside of warranty, can try the above, or attempt to use an ethernet connection (if equipped on your RokuTV) as an alternate route to wireless. Not all RokuTVs have an ethernet port, though.
I finally found a fix that works. The issue is that my internet service provider (CenturyLink) router/modem DHCP name special character state had to be re-configured to allow special characters.
In your computer browser go to your modem/router configuration. The IP address, Admin user name and password is usually on a sticker on your modem/router.
Go to "Advanced Setup,"
Go to "LAN settings,"
Go to "DHCP settings,"
Go to "Option 4-set DCHP name special character state,"
Click "Allow Special Characters,"
Click, "Apply,"
My Hisense Roku TV immediately connected and has stayed connected. Once after a power outage, I had to repeat the process.
Good Luck