You haven't suffered a legally cognizable harm because you got your money back, before you even had a chance to complain, so you have no basis for a lawsuit.
For what it is worth, pretty much every adult in the United States was affected by the Equifax breach. Also, usually Equifax wouldn't have had access to full bank account numbers in the first place, so that is an unlikely source of the problem.
You could open a new account and close the old one (as suggested by @mkennedy in the comments) because then if anyone had access to your bank account number and was abusing it, they could no longer do so.
The fact that it only happened once rather than involving many transactions, which is what you commonly see when there is a true identity theft, however, suggests a more benign possibility. There is a pretty good chance that this errant transaction which was reversed was simply a clerical error involving an inaccurate typing in of an account number that got your number instead of the intended one and was reversed when the money didn't leave the intended account (in contrast, identity theft incidents are almost never reversed without a complaint from the account holder). In other words, this may have simply been the banking equivalent of dialing the wrong number by mistake.
If this happens again, you should definitely shut down the account, but so far, it seems more likely that this was a one off clerical error. Humans are just not built to input scores of fifteen digit numbers on a daily basis in a 100% accurate fashion. As long as this job is in the hands of humans rather than computers or robots, the humans are going to make mistakes.