Write a note at the end of your latest chapter. You could say something like, 'Hey, check out my friend's novel! It's about…'
I've never seen anyone do it before, and there aren’t any rules saying you can't
I noticed someone publishing a cultivation novel here and on other sites it has 500 chapters. I think… they might have stolen it. https://www.scribblehub.com/series/1408601/if-i-let-you-be-the-clan-leader-you-only-accept-the-protagonist/
My condolences? Maybe you can ask them why? Their profile shows that your novel is the only one they've read. They might have accidentally given it a one-star rating. By the way, I gave you five stars! Hope your novel does really well!