Just ignore these guys. It's just that you are better than them and they lost. Don't worry about it :). Unless and until you are a well known good player (such as a YouTuber) you will always be called a hacker. It has happened to me so many times and people still don't know how to 1.9 PvP. Just ignore and carry on. If you yourself know you are not hacking, thats enough in itself, don't worry about what others think <3