Your Sonos products are probably looking for your old wireless network. Have you tried resetting all of your Sonos speakers and redoing the setup process?

Or setup your new router to broadcast same SSID and with same password as your previous router. This will prevent your playlist from being deleted.

Thank you for your reply.

actually I was connected before to the WiFi complex I live in.

now I did subscribe to an home internet box.

so I could not do this manipulation.

May I ask the process if ever I want to proceed by resetting my system?

https://support.sonos.com/s/article/1096?language=en_US

That would be the only way otherwise to change WiFi?

You can try going to System > Network > Wireless Setup in the Sonos app first.

Make sure your new router broadcasts 2,4 GHz b/g

https://support.sonos.com/s/article/126?language=en_US

Some routers do not bridge 2,4 and 5 GHz. You could try disabling 5 GHz in the router and see if that helps, and also try again with your Arc connected directly into the router by ethernet. 

Thank you for your advice 

my router support 2,4 and 5ghz

i did try to plug my Sonos arc as well directly but not plug in power since not enough length with the wire 

I just did follow this step from the apps but still the problem haven’t been solved...