This sounds like a creative way of scamming a pay-per-call advertiser. But, I can't imagine any of the 'big boys' in the pay-per-call market risking something like this.
Or, it could be competitors doing a denial-of-service attack on inbound calls, or a marketing-budget-depletion-attack on a pay-per-call campaign.
One way to deduce more: were the numbers he called the most commonly-advertised numbers for the target businesses, or other numbers through some tracked dispatch?
"...all you are doing is calling a company that we provide the number for, pressing the correct (1) or (2) – which we specify..."
If I'm interpreting that right, they're using inside information to get him up the phone tree to the right person (whatever their definition of "right" is).