The first thing to check is to make sure you are connected to the genuine Roku web site. This sounds suspiciously like you are on a scam site. You should be on this site only: https://my.roku.com/link and don't believe what the browser tab says. Make sure that's the exact URL you are on.
If that checks out OK, the next thing to try is using an alternate Internet source. The most successful reports have used a phone hotspot. Connect your Roku to the hotspot and use that until the activation is completed.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
