1. Don’t disable the “WiFi” on Sonos devices, unless there are extreme circumstances and you know what you’re doing. It doesn’t disable “WiFi”; it disables SonosNet.
2. Your router could well be confused. Look in Settings/System/About for whether your Amp shows WM:0.

Often a router won’t update the internal data with all changes.

A router reboot is often needed to see your external changes shown on the internal web pages.

Adding to the above that “disable WiFi” doesn’t disable WiFi, it turns off the whole radio 2.4 and 5 GHz causing much frustration to folks that expect their Sub and/or Surrounds to still work.

thank you for your answers.. i reset the router i tried two new network cables but still the same thing happens sonos amp only connects via wifi

So does the Amp show WM:0? If it does your router is wrong.

Hi, shows wm:0....

Your router is confused. The device is connecting via a wired path, or over SonosNet. 

Hi, thanks for your reply..I don't have SonosNet only sonos amp..I have asus RT-AX55 and I have reset it many times but always the same :(

You don’t have a SonosNet wireless signal if you disabled the radio on the wired device. However it’s still in ‘wired’ (i.e. SonosNet) mode, hence the WM:0.

ASUS devices show everything they can see on the subnet, wired or wireless. If it’s showing that Amp as being on a WiFi segment it’s confused. 

I just turned off the wifi on the asus, the sonos amp appears to me as if it is set to wifi 2.4 and it works normally , it must be that my asus is confused :)

Reboot the router. 

I've done it many times and it's always the same, I think I'll give up on this and leave it as it is, maybe it will resolve itself :)