Advertising is a long shot stock, I see no ethical dilema at all. However had they said sure, we will bring you 100 more customers, a problem exists. Otoh, if all they said was we'll create some content, air it 50 times for X price, no ethical issues at all imho. They did what they said.
It should be obvious to all that one doesn't succeed in media advertising overnight. It takes iteration, repitition, targeting, stats, and a ton of work, time, and money. To not understand this from a business standpoint, would not be unlike those who believe you can create a web site, and have people ordering product from it overnight making you a millionaire while you sleep. It's not going to happen, well maybe in the early days for a very few, but as a rule not without a lot of
SEO, advertising, work, time, and money.
Then again, in fairness, there are those companies that do prey on people outside of their area of expertise. Some of it no doubt is intentional, in other cases, one just gets used to the fact that everyone knows, so its never discussed or brought up, and then inocent folks suffer despite the best intentions on both parties.
What makes me wonder is their surprise at the lack of response.... It seems fishy to me.... first pass of 50 with a super low budget, on the first content iteration, no focus group testing, no demographics or stats data.... no surprise here at all.
I'd get together with a score guy, you might find one who used to be in the tv advertising business through email counseling. Then at least you can get some good education as well as what you need to do, and what not to do. They might be able to rework your content, or give you some good pointers as to appropriate targeting demographics.
As any FYI, one of my old colleh alumni used to work with a division of CBS that handled advertising. As far as content creation goes, 50 times what you paid was not out of line for 60 second audio only. (Yes, I fell on the floor too) Its not the equipment or studio time one is paying for. Its the people behind the equipment and their finely honed skill sets that make the difference.