It was Equifax that had the data breach, not Experian. Equifax was fined $700 million. Experian benefitted from the breach though since Equifax provided Experian credit monitoring services to those whose data was released.

Equifax stock has gone up since the 2017 data breach, though because consumers are not customers of Equifax, it's banks and lenders who are not concerned with data they don't control. If hackers had broke into Equifax and changed people's credit scores, the banks might have been a bit more concerned.