Hi Kevin,
If, as you've suggested, the fraudulent activity came through your ad campaigns, you might want to check out NS8. They offer multiple solutions, including to block advertising fraud, and to block order fraud. Probably worth having a conversation with their team.
There are some systems that can help to audit your historical data from Google Ads and other ad networks in order to help you dispute some of the traffic you spent money on, but prevention is a more logical approach for the long-term.
Best of luck!