It seems to me that there is a difference between "the law did not say you couldn't do it" and "it was legal." These are not identical propositions, and many things are completely illegal even though they have never been attempted before and haven't been regulated. The ensuing lawsuits (or class action suits) may well determine that these procedures were never legal and that damages have to be paid out, even though technically the law did not specifically say the companies couldn't do it. The incomplete letter of the law is not the entirety of what would determine the legality, to say nothing of the ethics, of raising prices like this.
IMO this situation is also partially a result of the current established practices of automatic withdrawals for electric bills, which I assume are not required by the companies in Texas any more than they are where I live. The people involved could no doubt have signed up for manual bill payment each month, at which point if they received a bill to that extent they could contest it in court rather than pay. But taking an automatic withdrawal of such shocking amounts without permissions smells to me also of a legal infraction, because if I had to guess (and the lawyers here can chime in if my guess is dead wrong) there is probably a legal standard of expected usage of the automatic withdrawal agreement. That is, there's an implicit understanding between client and company that you are agreeing to automatic withdrawals to facilitate regular monthly payments, and not to withdraw any amount you see fit to bill for services rendered. Billing unusual amounts to an automatic payment contract should be considered as fraud IMO, whether or not it in fact is fraud. It's implicitly a breach of contract for the initial purpose of signing up for automatic payments, and possibly grand larceny if it is in fact the case that it's illegal to withdraw arbitrarily high amounts of funds from someone's bank account after having obtained access.
Whether or not my opinions match what the law actually states, I would be displeased to learn that none of the above is accurate...