Try to get a business name and share it with the readers. By federal law this name cannot be withheld. Send the collector a cease-comm notice via USPS Certified with return card. The FTC and many consumer watchdogs explain how to draft one. This will set a legal landmine, as such a notice is ignored at their peril. Canned calls to mobile phones can get you a statutory payout, as well.
Learn how to exercise your FDCPA rights as an alleged debtor at FTC-dot-gov.