As people on here have said. It is best to just ignore them. Besides if they're christian then I'm sure there are alot of things you could say back to them if you so desired. Also in regards to being called a 'Furfag' that's like the oldest insult in the book of furry insults. (if there isn't a book there probably will be at some point) If they call you that then just reply 'so?' I feel sorry for their brain cells if that's the best that they can come up with. Just think to yourself. It's only a word, and a pretty dumb one at that. If you cant make friends in that school then why not try and make friends outside of school? Get a hobby, go to events. I'm sure you'll meet people that way, and if you do then you have something in common and grounds to strike up a conversation.
Mate, just think about the future. it gets better.