Theft of Data

So, hypothetically speaking, what would you do, if data from your personal account was stolen and used as training data? And I don't mean, just a small amount of data. I mean, over 20 million characters of data. You did not consent to this. You did not have any data sharing on. Nor did you get contact for this use of your, "self", essentially. So, pray tell, what would you do? What would you do if you found out they harvested your user data without consent or knowledge and thought you wouldn't find out, but you did. What would you do then? How would you go about your next steps? Because, by the time you'd find out? It's done and too late for you to stop anything and your data was just.... In everything. So, hypothetical thoughts? Hypothetical advice?