This "faith in the law" is libertarianism's biggest weakness, and the reason why the older I've gotten, the more appealing anarchism has become. The ways we see the law working in this case, are just the ways that law actually works. Screw the little guy and protect the big man? A feature, not a bug!
The reasonable way to oppose unfairness is to actually oppose unfairness, not to imagine that some contingent and evolved phenomenon called "law" is going to magically give us what we want. If utopia comes and police are devoted only to the enforcement of contract, those entrusted with interpreting contracts will be our rulers. Those in power, will exercise power. This recursion can't be defined out of existence.
But the original comment I responded to seemed to imply that the libertarian theory would allow this "free market" behavior, which is not the way libertarians see it.
In this case, the bank charged customers for services they never requested. That is fraud. It has nothing to do with "free markets" as defined by libertarians.
If you find some libertarian scholarship, you will also notice that libertarians see contract enforcement as a vital role of government. This would also be a breach of contract.
Libertarian != Anarchist :)