Unplug all Sonos devices again, and while they are unplugged, reboot your router. When the router comes back up, plug back in the Sonos.

If they’re still not showing, there may have been an update to your router that turned off the 2.4Ghz channel, it may be worth checking that it is still sending one.

You can always wire one Sonos device (not a bonded surround or Sub) to your router, and it will create a SonosNet network that all devices will connect to after a minute Ir two, once the software recognizes it exists, but if you go that route, be certain to then read the Removing Wifi data FAQ. You’ll want to avoid having two separate methods for your Sonos devices to connect. 

Thanks Bruce, unplugging the speakers and rebooting the router worked.

Ok so it worked for a few days but now the speakers won't pick up again. This is very unimpressive, are Sonos releasing a fix?? Expensive speakers that can't be controlled from a phone. Really poor

I’m not sure this is a Sonos issue, but more likely a network issue.

Sometimes the router can hand out duplicate IP addresses, e.g. after an update of the Sonos software. Rebooting the system in the correct order as specified by Bruce above may help for now, but if you assign fixed IP addresses for your Sonos units within the routers DHCP tabel, you may be able to prevent this problem in the future.

Restart your controller, too.

Interference on your wifi network can also cause severe trouble, see this article:
https://support.sonos.com/s/article/3286?language=en_US