no way to factory reset sonos ace

Are you following these instructions?

https://support.sonos.com/en-us/article/reset-your-sonos-product

Make sure you are using a power brick, o e with adequate power and not a computer, tablet or phone for power.

If that fails, are you in your free return window?

My Ace have no issues factory reseting using the above so yours should also work. 

​@Stanley_4  
Thank You for advice.
 try two ways from charger and USB port in PC as well  - the same fail

The PC option can be a problem as the connectivity features can disrupt the reset.

Is your charger at least 15 Watts? That is a minimum, I use a 25 or 40 Watt one here.

https://support.sonos.com/en-us/article/charging-your-sonos-ace

It’s not just you; I have the same problem. I’ve been trying for over an hour to factory reset and the headphones just keep turning on and off no matter how long I hold the button and in what order I plug in the powered usb-c cable, I never see any blinking lights. My app recognizes it as a “new device” now but my bluetooth recognizes them by an old name, so there’s no confirmation they’ve been “factory reset” after all, and I still have issues with the sound quailty via my Mac OS (no issues with my phone).

Have you called Sonos Support directly to discuss it? They’d likely be able to help identify if there is an issue with your Ace. 

Unfortunately I don’t really have time to do that. I’ve just had to learn to live with all the bugs, like the side button not pausing and starting my music anymore. That’s a fun one.