I’ve had this too! When I wrote my first story in ink I got a negative fan-mail saying I had copied a popular story at the time called Whiskey or something like that.
The only similarities were that we had a Female MC and were both in Fantasy 
You have to take things like this with a pinch of salt because let’s be honest, it’s difficult not to have similarities with other people’s stories in one way or another.
They were probably just having a bad day or were trying to be annoying 