I don’t have any experience with your ISP, but just to try to assist you here. If you do already have an existing Sonos system that worked with your old ISP, what happens if you wire a single (non-factory reset) Sonos device to your new router and power-cycle your other Sonos devices? - do they then show up in your Sonos App when your mobile controller device is connected to your new WiFi network?

They did show up but wouldn't connect over WiFi. I've factory reset a few times since. I can connect over ethernet but whenever I try to change the network settings to WiFi it won't connect.

Is the new WiFi network SSID currently shown as listed in your network settings in the Sonos App? …Settings/System/Network/Manage Networks

If the SSID is not present in the Apps network settings, then wire a (non factory-reset) Sonos product so that it appears in your Sonos App, then bring all your other non-reset speakers online too using their SonosNet connection. When all are visible in the App, then add the new WiFi network to ALL using the ‘Update Networks’ tool (that’s also located in Settings/System/Network/Manage Networks).

When the network has been added, then see if the devices will then connect to your WiFi. If you did reset any of your devices, do not use those as the wired device (important) otherwise you may lose your original system setup and all your previous settings - so only use a non-factory reset device as the wired device. If you did reset a device you may need to add that back to your original system once you have things back up and running, but maybe set such devices aside for the time being until you have your original system back online.

It might be that the Wi-Fi signal being used by the new device is not compatible with Sonos’ Sonos Network Requirements , it may be worth logging in to the router to see what type of signal is being used. 

The oare the router specs

It has a "backup" 4g WiFi when the WiFi 6 drops. I think that is the LTE component.  Could that be the issue?

Specifications

WiFi:

• WiFi 6 (802.11ax)
• 2.5GHz – 4x4 Antenna
• 5GHz – 4x4 Antenna

Memory:

• 1GB Storage Memory
• 1GB Flash Memory

LTE: 

• CAT 12 - Qualcomm

LTE Speed:

• 25Mbs Down 5Mbs Up

WiFi Certified:

• WiFi Alliance Certified

Check that the 2.4Ghz WiFi network band is 802.11b/g/n compatible as stated in the Sonos specifications and for now, I would set its security mode to ‘WPA2 personal’

To help cut down on interference too, you could also optionally set its channel-width to 20Mhz only. See if that then sorts your issue.

The LTE (mobile) connection you mention is a fallback WAN connection for those ‘hopefully’ rare occasions when your ISP is offline - that should not affect the problem you’re seeing currently with setup and is only ever relevant if your ISP connection is offline anyway.

Thanks for your help. 

I've change security to to WPA2. WiFi mode is now set to 803.11b + g +n and bandwidth to 20MHz.

Should I disable band steering?

I would see if you can get things to work with-band steering in place first of all.

Still not connecting. Should I try a different phone and setup a new profile with a new email?  I've been following all the Sonos steps and one step I have ignored was to try a different mobile device. I'm using a pixel 7 pro. Surely that is not the problem. Running out of ideas

If you have another mobile device to hand it maybe worth trying that, but if not, you maybe best to call Sonos Support Staff and see if they can perhaps assist you to resolve the matter. Here is a link to get in touch… 

https://support.sonos.com/s/contact

So I used my iPad and it worked without a hitch. What a world.

Thanks all!

If you do solve the issue with the Pixel Pro 7 - then please post back and let us know what it was, as that might prove useful to others here in the community too. (Thanks) … and glad to hear you’re otherwise up and running with your system. 

I don't think I'll ever solve it with the pixel 7 pro now. It does work with the pixel now just couldn't do the setup. When I did it with the iPad I had both speakers setup in a few minutes. With the the pixel 7pro a spent weeks and was a day away from selling the Sonos kit and switching to proaudio.