Apple Watch 6 screen went black

Just got my Apple Watch 6 for one week, and after I removed it to sleep, the screen went black. I tried to force restarting several times, checked if the voiceover and screen curtain both are turned off, nothing has worked so far.

Unpaired and erased all content as instructed, same, nothing.

My iPhone recognizes the watch and keeps me telling to pair it, but since I have a black screen I'm unable to.

I can rear the apple watch working, even can turn on and off the voiceover, but the screen remains black.

Can anyone give me a suggestion?

Thank you