Yes, the USCIS has every right to investigate to determine if somebody entered the nation under false pretenses, or... whatever is alleged. There are plenty of cases where people pay money to marry somebody then fake their way through the LPR process (they even made a movie about that particular scam, some years back) - if the USCIS finds out that somebody attempted such a fraud, it's more than reasonable for them to say, "Sorry, you're no longer welcome in the United States."

As we don't know the background of your case or the substance of your ex-spouse's allegations, we cannot comment on your personal situation. If you're interested in fighting the allegations or how they might affect you in the future, consult an immigration lawyer with the details.