my parents fucking lied
talking to strangers on the internet was the best decision of my life
Your work is copyrighted the moment you write it down. However, it’s very difficult legally to force someone to change their stolen material if they are not making any money off it (such as stealing fanfic plots, etc).
You do have the right to ask them to change it, especially since your proof is that your version existed first. If you posted it online, you have the dates and sources to show that yours was the first version to exist. If they refuse, you can contact the administrators of the website they’re posting it on with proof that they are plagiarizing from you. If that’s not an option, you are within full right to let everyone know that it is being stolen from you if they refuse to take it down.
No one likes plagiarizers. Don’t hesitate to call it out and try to get the writer to take it down. It’s not fair to you, and it’s not fair to people who are reading the work.
I’m so glad flappy bird ended before there was legitimate merchandise made like angry birds