I'm really sorry that our having to deal with this, it's hard and I know from personal experience.
The best advice have to give is to ignore it. It's hard ecspecially when they are cursing at you, but just try to laugh at them. They're just upset that you got the credit you deserve for making a great project.
If you ever feel like saying something back never ever make it rude in any way. Just be calm and polite. Whoever this is, is looking for your reaction to this. So, give them a nice reaction.
Just say something like: "Hey, I see you're upset with me. I know it may have looked like I copied but it was 100% not intentional. I apologize if you think I copied." Then just exit and don't reply again. Don't fuel the flames :)
If it continues email either t1 or Liza.
(Tracey@gethopscotch.com & Help@gethopscotch.com/Liza@gethopscotch.com)