Let's go back to our stock market example for a moment. The nature of the stock market is to go up and down over time. The trick is to pick stocks that rise over the long haul. The same is true of advertising. You can't place a single ad in the newspaper or on radio and determine advertising doesn't work if that single ad is not successful.
Advertising takes time to produce results.
People need to be exposed to your ad over a period of time for it to be successful. If you are using radio I would suggest scheduling ads every week for at least four months. And at lease three out of every four weeks after that. Many small town radio stations are very inexpensive. If you can't do what I suggest then do as much as you can.