@Krystal16
So sorry this has happened to you. I agree with @Alexandra316 that you should try to have the review removed. I'm not saying you will have much success (I am sure there used to be something about defamation in the content policy, but I can't see it now) but it might be worth a try, especially if the correspondence with the guests demonstrates the issues which caused you to ask them to leave. By the way, did you report these guests to Airbnb when you decided to end their stay?
The only time I was called racist was by a potential guest when I wouldn't accept her booking. She told me I was racist against Asians. She had automatically assumed this until I told her I WAS Asian, as were my current guests and the majority of my guests and explained again the reason why I was not accepting her booking (the cancellation policy for South Korean guests). Finally, she understood and said no problem.
Sounds like your guests are playing the race card, or maybe they just genuinely believed that their behaviour was acceptable and couldn't find any other explanation for your decision. Unfortunately, the guilty party doesn't always see themselves as guilty! A lot of people think if they book and pay for an Airbnb, they can behave however they like.