Anyone can attempt to file a FreightGuard report, but that doesn’t mean it will automatically stick without scrutiny. False reports can be disputed, especially if you’ve never done business with them. Keep all screenshots and communication as proof.
I’d contact FMCSA, DAT, and Carrier411 (if applicable) right away and alert brokers you regularly work with about possible MC impersonation. Make sure your contact info in SAFER is accurate and locked down.