Each dollar you spend on a Facebook Ads is not being used to reach the people you want.
A fake user could be clicking on your ads. Maybe a bot impersonating a user. Maybe you are targeting people who already bought your product. Maybe it is just people who are tired of seeing your ad, not interested, not in the right mood.
All of these cases are sunk costs. Money spent and permanently lost.
There is no point on trying to get those dollars back. What you can do is to refine your audience. Use custom audiences to exclude people who are your customers already (if you are running a prospecting campaign.) Refresh your Ads (texts/images/videos.) Use FraudSensor in your landing pages to detect bots’ traffic coming from Facebook.