How exactly did you do this and for what product?Briefly held a marketing position in which we did this.
It can provide results if you're persistent+patient. You will get a lot of annoyed, confused people but you will also get those who if explained what is being sold will be legitimately interested.
I've hired call centers for 2 businesses, one for direct sales, one for customer feedback. Neither produced enough results to return a positive ROI. I gave each an honest chance at working, 90 days +.
If you're looking for product sales, I found direct response ads work best (for offline endeavors) on a consistent basis over long periods of time. With the advent of the Internet, direct response ads in publications have become less and less costly, and they tend to have great information of their demographics. They're also somewhat flexible on ad-spend if you tell them that you're only interested in a specific segment of their demos they will work with you on ad-spend. For example, if I'm only interested in 80% of their demographics, I'll hardball to only end up paying 80% of their after-discount rates for the ad space. Get the discount first (they always hit you higher), then address the demographics.
If you just want lead generation, I have found buying leads from reputable brokers within your specific market segment as a more fruitful endeavor.
Hope some of that helps.
what sort of leads were you buying? What were you paying per lead/making per lead on average?
There are results if what you're selling fits what most people need. You also need to have a great attitude and sound believable. It will take some time at first, but you can work your way up to success.