I've got an elderly relative who fell into something that I swear followed a lead generation funnel. Accepted some semi-legitimate domestic computer services help (optimize your PC and scan for spyware by some company from Utah), only to have the full hammer come down a few weeks later with a follow up from an Indian call center that commandeered her PC, made fake deposits to her bank account, turned on her camera and showed he could see everything, and insisted she purchase $500 in iTunes cards to pay for the malware removal. After wising up, the same center called her multiple times daily for more than a year from various spoofed numbers.
If they're getting calls every 30 minutes, it's likely they've become a qualified lead in some way, by something they've done.