In the Sonos app did you remove surrounds and sub from the surround room before changing ISP?  A number of folks on this community suggest using the same SSID / password you used for the old ISP.

I did not even think about it at the time. And the change happend like about 6months ago, I've just not tried to fix it until now, so I dont rember the SSID or password of the old one. I get this, and I`ve tried to select the sub+speaker system and tell it to forget it, but that dosent seem to work. and I can seem to connect the playbar to the other either.

 So all the speakers were factory reset… Right?  Odd that the Ones-Sub would be shown in a Sonos System.  Sounds like you need to start over as though you just bought the speakers new.  Also seems like there should not be two separate Sonos systems.

 Maybe the app needs to be deleted then re installed to start from scratch.

Yeah, that’s what I’ve been trying to do, gave up for today though as my phone was running out of power but will give it another go tomorrow, probably try to another full factory restart and delete/reinstall the app

You have set up two systems by mistake. Only the Playbar is in Sonos System (2); the other speakers are still in Sonos System (1). 
Reset the speakers other than the Playbar and then be sure to add to existing system when you add them to the Playbar system. 

I’m struggling to get the app to forget all of it, I’ve done the hold the buttons while plugging in the power, but they still pop up as a system. I’ve tried to select the system, then go into manage and go to Forget system, but is seems it does nothing. I can also only find any of the systems whenever I plug in an ethernet cable, but I can’t have it cabled normally, I have to move everything closer to the router

Power off your phone. Reset the speakers except playbar. Connect Playbar to router by Ethernet cable. Start your phone and you should see your Playbar. Ensure WiFi is enabled. Power up a One and add to system. Repeat for other. Add them as surrounds.