I wouldn't particularly call this "stealing my idea" but it was definitely a coincidence to end all coincidences.
I love creating fictional worlds and characters. Usually I base them around worlds in a particular blocky game. When I was younger, I had a specific world/project named Elementia. I know, not really original, but wait a second. One day, I was walking through my library and I see a book. A book ABOUT a story taking place in the game called ELEMENTIA. I couldn't believe it. I actually had to google it recently to see if it was just my imagination but nope, it was real. Ticks me off to this day.